C# Interfaces

An interface is defined as a syntactical contract that all the classes inheriting the interface should follow. The interface defines the ‘what’ part of the syntactical contract and the deriving classes define the ‘how’ part of the syntactical contract.

Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to define the members. It often helps in providing a standard structure that the deriving classes would follow.

Abstract classes to some extent serve the same purpose, however, they are mostly used when only few methods are to be declared by the base class and the deriving class implements the functionalities.

Declaring Interfaces

Interfaces are declared using the interface keyword. It is similar to class declaration. Interface statements are public by default. Following is an example of an interface declaration −

public interface ITransactions {
   // interface members
   void showTransaction();
   double getAmount();
}

Example

The following example demonstrates implementation of the above interface −Live Demo

using System.Collections.Generic;
using System.Linq;
using System.Text;
using System;

namespace InterfaceApplication {
   
   public interface ITransactions {
      // interface members
      void showTransaction();
      double getAmount();
   }
   public class Transaction : ITransactions {
      private string tCode;
      private string date;
      private double amount;
      
      public Transaction() {
         tCode = " ";
         date = " ";
         amount = 0.0;
      }
      public Transaction(string c, string d, double a) {
         tCode = c;
         date = d;
         amount = a;
      }
      public double getAmount() {
         return amount;
      }
      public void showTransaction() {
         Console.WriteLine("Transaction: {0}", tCode);
         Console.WriteLine("Date: {0}", date);
         Console.WriteLine("Amount: {0}", getAmount());
      }
   }
   class Tester {
     
      static void Main(string[] args) {
         Transaction t1 = new Transaction("001", "8/10/2012", 78900.00);
         Transaction t2 = new Transaction("002", "9/10/2012", 451900.00);
         
         t1.showTransaction();
         t2.showTransaction();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Transaction: 001
Date: 8/10/2012
Amount: 78900
Transaction: 002
Date: 9/10/2012
Amount: 451900

C# Inheritance

One of the most important concepts in object-oriented programming is inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and speeds up implementation time.

When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.

The idea of inheritance implements the IS-A relationship. For example, mammal IS A animal, dog IS-A mammal hence dog IS-A animal as well, and so on.

Base and Derived Classes

A class can be derived from more than one class or interface, which means that it can inherit data and functions from multiple base classes or interfaces.

The syntax used in C# for creating derived classes is as follows −

<acess-specifier> class <base_class> {
   ...
}

class <derived_class> : <base_class> {
   ...
}

Consider a base class Shape and its derived class Rectangle −Live Demo

using System;

namespace InheritanceApplication {
   class Shape {
      public void setWidth(int w) {
         width = w;
      }
      public void setHeight(int h) {
         height = h;
      }
      protected int width;
      protected int height;
   }

   // Derived class
   class Rectangle: Shape {
      public int getArea() { 
         return (width * height); 
      }
   }
   class RectangleTester {
      static void Main(string[] args) {
         Rectangle Rect = new Rectangle();

         Rect.setWidth(5);
         Rect.setHeight(7);

         // Print the area of the object.
         Console.WriteLine("Total area: {0}",  Rect.getArea());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Total area: 35

Initializing Base Class

The derived class inherits the base class member variables and member methods. Therefore the super class object should be created before the subclass is created. You can give instructions for superclass initialization in the member initialization list.

The following program demonstrates this −Live Demo

using System;

namespace RectangleApplication {
   class Rectangle {
      
      //member variables
      protected double length;
      protected double width;
      
      public Rectangle(double l, double w) {
         length = l;
         width = w;
      }
      public double GetArea() {
         return length * width;
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle  
   class Tabletop : Rectangle {
      private double cost;
      public Tabletop(double l, double w) : base(l, w) { }
      
      public double GetCost() {
         double cost;
         cost = GetArea() * 70;
         return cost;
      }
      public void Display() {
         base.Display();
         Console.WriteLine("Cost: {0}", GetCost());
      }
   }
   class ExecuteRectangle {
      static void Main(string[] args) {
         Tabletop t = new Tabletop(4.5, 7.5);
         t.Display();
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 7.5
Area: 33.75
Cost: 2362.5

Multiple Inheritance in C#

C# does not support multiple inheritance. However, you can use interfaces to implement multiple inheritance. The following program demonstrates this −Live Demo

using System;

namespace InheritanceApplication {
   class Shape {
      public void setWidth(int w) {
         width = w;
      }
      public void setHeight(int h) {
         height = h;
      }
      protected int width;
      protected int height;
   }

   // Base class PaintCost
   public interface PaintCost {
      int getCost(int area);
   }
   
   // Derived class
   class Rectangle : Shape, PaintCost {
      public int getArea() {
         return (width * height);
      }
      public int getCost(int area) {
         return area * 70;
      }
   }
   class RectangleTester {
      static void Main(string[] args) {
         Rectangle Rect = new Rectangle();
         int area;
         
         Rect.setWidth(5);
         Rect.setHeight(7);
         area = Rect.getArea();
         
         // Print the area of the object.
         Console.WriteLine("Total area: {0}",  Rect.getArea());
         Console.WriteLine("Total paint cost: ${0}" , Rect.getCost(area));
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Total area: 35
Total paint cost: $2450

10 znakova da je vaš laptop zaražen virusom

Oglasi

U najgorem slučaju neće biti nikakvih znakova. No, u pravilu se na vrijeme može primijetiti da neke stvari nisu kakvima bi trebale biti.

1. Laptop je spor k’o puž

Spor laptop jedna je od najčešćih nuspojava virusa i ostalog malwarea. Naravno, postoji više razloga zašto laptop radi usporeno – premalo RAM-a, preslab procesor za zadatke koje želite obaviti, pun hard disk itd.

Međutim, ako primijetite da je laptop preko noći postao spor do neupotrebljivosti, moguće je da ste ga negdje zarazili. Otvorite “Upravitelj zadataka” (Task manager) tako da na tipkovnici pritisnite istovremeno CTRL + ALT + DELETE. Tamo se nalazi popis svih aktivnih procesa na vašem računalu. Provjerite odlazi li previše procesorske snage na sumnjivu aplikaciju.

Oglasi

2. Skočni prozori na sve strane

Još jedan znak moguće zaraze virusom ili nekim drugim malwareom su pop-up ili skočni prozori koji se pojavljuju neočekivano i u neprirodno velikom broju.

Ako par komada iskoči na nekoj web stranici, to ne znači da imate zaraženi laptop. Međutim, ako je njihov broj puno veći i pojavljuju se čak i kada ne surfate internetom, vrlo vjerojatno se na vašem laptopu nalazi tzv. adware. Riječ je o programu koji svoje žrtve bombardira reklamama. Nekad se radi o oglasima za legitimne proizvode i usluge, no često sadrže linkove na stranice koje će na vaše računalo probati skinuti još štetnih programa i virusa.

U slučaju zaraze adwareom, nipošto nemojte kliknuti na poveznice u reklama ili skidati programe i datoteke koje ste tamo pronašli. Time ćete napraviti još veću štetu.

Oglasi

3. Datoteke i programi magično nestaju

Nikako ne možete pronaći onu tablicu u excelu ili slike s godišnjeg za koje ste sto posto sigurni da ste ih spremili?

Brisanje različitih datoteka, uključujući i sistemske datoteke, jedna je od mogućih posljedica zaraze malwareom. Nestanak sistemskih datoteka prepoznat ćete tako što se neki programi ili neće htjeti pokrenuti ili će loše raditi, a dobit ćete i obavijest da nedostaje neka od datoteka potrebnih za ispravan rad programa.

Osim brisanja datoteka, malware ih može i kriptirati. U tom će se slučaju datoteka nalaziti gdje bi trebala, ali je nećete moći otvoriti.

Oglasi

4. Nova početna stranica u web pregledniku

Vaš web preglednik (Chrome, Firefox, Edge) neobično se ponaša? Odjednom početna stranica više nije Google, Bing ili neka druga poznata tražilica koju koristite, već stranica koje se ne sjećate da ste je ikad prije posjetili. Na alatnoj traci pojavile su se nove oznake, mini tražilice ili ekstenzije koje niste sami skinuli.

Ova dva scenarija samo su neki od mogućih znakova zaraze. Najčešće se dogode slučajnim klikom na link ili skočni prozor koji pokreće preuzimanje i instalaciju neželjenih i potencijalno štetnih programa.

Oglasi

5. Laptop se gasi sam od sebe

Usred ste sastavljanja e-maila, kada se vaš laptop iznenada zamrzne ili, još gore, ponovno pokrene ili ugasi. Računalo će to rijetko raditi samo od sebe, osim ako nemate zakazano ažuriranje i potrebno je ponovo pokrenuti računalo da bi se ta ažuriranja aktivirala.

Ako se laptop ponovo upali ili ga sami možete upaliti pritiskom na power gumb, imate sreće. Odmah pokrenite antivirusni program i probajte pronaći uzrok. U slučaju da se laptop više ne da pokrenuti ili se neprestano gasi i pokreće, morat ćete ga odnijeti u servis.

Oglasi

6. Dobivate upozorenja o zarazi, a nisu od antivirusnog programa

Upozorenja šalju lažni antivirusni programi, a donose unosnu zaradu. Funkcioniraju tako da se instaliraju na vašem računalu te prikazuju prijetnje o zastrašujućim virusima kojih tamo zapravo nema. Potom će vam ponuditi da kupite dodatnu zaštitu koja će ukloniti sve navodne prijetnje.

Upozorenja da ste zaraženi virusom mogu dolaziti i u obliku skočnih prozorčića dok posjećujete sumnjive stranice bez da je lažni antivirusni program instaliran na vašem računalu.

Upamtite da besplatni antivirusni programi koje velika većina nas koristi (kao što su Avast, Bitdefender itd.) nikada neće tražiti da platite prije provjere postoji li na vašem računalu prijetnja u obliku virusa i drugog štetnog malwarea. Ako se odlučite na plaćenu nadogradnju, dobit ćete proširenu zaštitu, ali ona osnovna uvijek je dostupna, čak i kod besplatnih opcija.

Ako neki program traži od vas da platite kako bi mogao ukloniti virus, riječ je o prevari pomoću koje netko želi zaraziti vaše računalo malwareom i zaraditi na vašem neznanju.

Oglasi

7. Nedostatak slobodnog prostora

Iznenada ste ostali bez slobodnog prostora na hard disku, a do nedavno niste popunili ni polovicu kapaciteta. Više je načina na koje maliciozni softver može popuniti prazan prostor na vašem laptopu, no često je namjera popuniti kapacitet hard diska kako bi se računalo srušilo.

Oglasi

8. Neuobičajeni zvukovi

Ako malware uzrokuje pretjerani rad procesora, pratit će ga zvuk vrtnje ventilatora čija je uloga ohladiti računalo tijekom povećanog rada. U slučaju da ventilator većinu vremena radi pod punim kapacitetom, to znači laptop ne radi kako bi treba, a jedan od razloga može biti i malware. Na probleme može ukazati i HDD koji se stalno vrti i proizvodi zvukove čak i kada niti jedan program nije pokrenut.

Više razloga može uzrokovati povećani napor hardvera laptopa. No, ako se to dogodi u kombinaciji s nekoj od drugih situacija na ovoj listi, možda je riječ o malwareu.

Oglasi

9. Velika internetska aktivnost kada ne surfate

Ostvareni mjesečni promet je drastično veći nego što bi trebao biti? Možda je na vaš laptop skinut i instaliran rootkit program ili neki drugi maliciozni softver koji će popuniti hard disk, usporiti računalo, instalirati adware itd.

10. Netko šalje mailove s vašeg računa, a niste vi

Ako vam se e-mail kontakti jave s pitanjima zašto im šaljete spam mailove s čudnim privicima i linkovima, moguće je ne samo da imate računalo zaraženo virusom, nego se pokušava proširiti i na druga računala koristeći vašu e-mail listu. Slična situacija može se dogoditi i s vašim Facebook ili Twitter računom.

Osim što trebate skenirati računalo antivirusnim programom, postojanje problema možete uočiti provjerom nalazi li se na vašem internet pregledniku ekstenzija koju niste instalirali.

Nikada nije neophodno naglasiti da brinete o zaštiti svojih online profila, a to uključuje snažne lozinke i oprez da se u njih ulogiravate isključivo na sigurnim uređajima i preko sigurnih mreža.

Oglasi

C# – What is a NullReferenceException, and how do I fix it?

What is the cause?

Bottom Line

You are trying to use something that is null (or Nothing in VB.NET). This means you either set it to null, or you never set it to anything at all.

Like anything else, null gets passed around. If it is null in method “A”, it could be that method “B” passed a null to method “A”.

null can have different meanings:

  1. Object variables that are uninitialized and hence point to nothing. In this case, if you access members of such objects, it causes a NullReferenceException.
  2. The developer is using null intentionally to indicate there is no meaningful value available. Note that C# has the concept of nullable datatypes for variables (like database tables can have nullable fields) – you can assign null to them to indicate there is no value stored in it, for example int? a = null; (which is a shortcut for Nullable<int> a = null;) where the question mark indicates it is allowed to store null in variable a. You can check that either with if (a.HasValue) {...} or with if (a==null) {...}. Nullable variables, like a this example, allow to access the value via a.Value explicitly, or just as normal via a.
    Note that accessing it via a.Value throws an InvalidOperationException instead of a NullReferenceException if a is null – you should do the check beforehand, i.e. if you have another non-nullable variable int b; then you should do assignments like if (a.HasValue) { b = a.Value; } or shorter if (a != null) { b = a; }.

The rest of this article goes into more detail and shows mistakes that many programmers often make which can lead to a NullReferenceException.

More Specifically

The runtime throwing a NullReferenceException always means the same thing: you are trying to use a reference, and the reference is not initialized (or it was once initialized, but is no longer initialized).

This means the reference is null, and you cannot access members (such as methods) through a null reference. The simplest case:

string foo = null;
foo.ToUpper();

This will throw a NullReferenceException at the second line because you can’t call the instance method ToUpper() on a string reference pointing to null.

Debugging

How do you find the source of a NullReferenceException? Apart from looking at the exception itself, which will be thrown exactly at the location where it occurs, the general rules of debugging in Visual Studio apply: place strategic breakpoints and inspect your variables, either by hovering the mouse over their names, opening a (Quick)Watch window or using the various debugging panels like Locals and Autos.

If you want to find out where the reference is or isn’t set, right-click its name and select “Find All References”. You can then place a breakpoint at every found location and run your program with the debugger attached. Every time the debugger breaks on such a breakpoint, you need to determine whether you expect the reference to be non-null, inspect the variable, and verify that it points to an instance when you expect it to.

By following the program flow this way, you can find the location where the instance should not be null, and why it isn’t properly set.

Examples

Some common scenarios where the exception can be thrown:

Generic

ref1.ref2.ref3.member

If ref1 or ref2 or ref3 is null, then you’ll get a NullReferenceException. If you want to solve the problem, then find out which one is null by rewriting the expression to its simpler equivalent:

var r1 = ref1;
var r2 = r1.ref2;
var r3 = r2.ref3;
r3.member

Specifically, in HttpContext.Current.User.Identity.Name, the HttpContext.Current could be null, or the User property could be null, or the Identity property could be null.

Indirect

public class Person 
{
    public int Age { get; set; }
}
public class Book 
{
    public Person Author { get; set; }
}
public class Example 
{
    public void Foo() 
    {
        Book b1 = new Book();
        int authorAge = b1.Author.Age; // You never initialized the Author property.
                                       // there is no Person to get an Age from.
    }
}

If you want to avoid the child (Person) null reference, you could initialize it in the parent (Book) object’s constructor.

Nested Object Initializers

The same applies to nested object initializers:

Book b1 = new Book 
{ 
   Author = { Age = 45 } 
};

This translates to:

Book b1 = new Book();
b1.Author.Age = 45;

While the new keyword is used, it only creates a new instance of Book, but not a new instance of Person, so the Author the property is still null.

Nested Collection Initializers

public class Person 
{
    public ICollection<Book> Books { get; set; }
}
public class Book 
{
    public string Title { get; set; }
}

The nested collection Initializers behave the same:

Person p1 = new Person 
{
    Books = {
         new Book { Title = "Title1" },
         new Book { Title = "Title2" },
    }
};

This translates to:

Person p1 = new Person();
p1.Books.Add(new Book { Title = "Title1" });
p1.Books.Add(new Book { Title = "Title2" });

The new Person only creates an instance of Person, but the Books collection is still null. The collection Initializer syntax does not create a collection for p1.Books, it only translates to the p1.Books.Add(...) statements.

Array

int[] numbers = null;
int n = numbers[0]; // numbers is null. There is no array to index.

Array Elements

Person[] people = new Person[5];
people[0].Age = 20 // people[0] is null. The array was allocated but not
                   // initialized. There is no Person to set the Age for.

Jagged Arrays

long[][] array = new long[1][];
array[0][0] = 3; // is null because only the first dimension is yet initialized.
                 // Use array[0] = new long[2]; first.

Collection/List/Dictionary

Dictionary<string, int> agesForNames = null;
int age = agesForNames["Bob"]; // agesForNames is null.
                               // There is no Dictionary to perform the lookup.

Range Variable (Indirect/Deferred)

public class Person 
{
    public string Name { get; set; }
}
var people = new List<Person>();
people.Add(null);
var names = from p in people select p.Name;
string firstName = names.First(); // Exception is thrown here, but actually occurs
                                  // on the line above.  "p" is null because the
                                  // first element we added to the list is null.

Events (C#)

public class Demo
{
    public event EventHandler StateChanged;
    
    protected virtual void OnStateChanged(EventArgs e)
    {        
        StateChanged(this, e); // Exception is thrown here 
                               // if no event handlers have been attached
                               // to StateChanged event
    }
}

(Note: The VB.NET compiler inserts null checks for event usage, so it’s not necessary to check events for Nothing in VB.NET.)

Bad Naming Conventions:

If you named fields differently from locals, you might have realized that you never initialized the field.

public class Form1
{
    private Customer customer;
    
    private void Form1_Load(object sender, EventArgs e) 
    {
        Customer customer = new Customer();
        customer.Name = "John";
    }
    
    private void Button_Click(object sender, EventArgs e)
    {
        MessageBox.Show(customer.Name);
    }
}

This can be solved by following the convention to prefix fields with an underscore:

    private Customer _customer;

ASP.NET Page Life cycle:

public partial class Issues_Edit : System.Web.UI.Page
{
    protected TestIssue myIssue;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
             // Only called on first load, not when button clicked
             myIssue = new TestIssue(); 
        }
    }
        
    protected void SaveButton_Click(object sender, EventArgs e)
    {
        myIssue.Entry = "NullReferenceException here!";
    }
}

ASP.NET Session Values

// if the "FirstName" session value has not yet been set,
// then this line will throw a NullReferenceException
string firstName = Session["FirstName"].ToString();

ASP.NET MVC empty view models

If the exception occurs when referencing a property of @Model in an ASP.NET MVC View, you need to understand that the Model gets set in your action method, when you return a view. When you return an empty model (or model property) from your controller, the exception occurs when the views access it:

// Controller
public class Restaurant:Controller
{
    public ActionResult Search()
    {
        return View();  // Forgot the provide a Model here.
    }
}

// Razor view 
@foreach (var restaurantSearch in Model.RestaurantSearch)  // Throws.
{
}
    
<p>@Model.somePropertyName</p> <!-- Also throws -->

C# – How do I create an Excel (.XLS and .XLSX) file in C# without installing Microsoft Office?

You can use a library called ExcelLibrary. It’s a free, open source library posted on Google Code:

ExcelLibrary

This looks to be a port of the PHP ExcelWriter that you mentioned above. It will not write to the new .xlsx format yet, but they are working on adding that functionality in.

It’s very simple, small and easy to use. Plus it has a DataSetHelper that lets you use DataSets and DataTables to easily work with Excel data.

ExcelLibrary seems to still only work for the older Excel format (.xls files), but may be adding support in the future for newer 2007/2010 formats.

You can also use EPPlus, which works only for Excel 2007/2010 format files (.xlsx files). There’s also NPOI which works with both.

There are a few known bugs with each library as noted in the comments. In all, EPPlus seems to be the best choice as time goes on. It seems to be more actively updated and documented as well.

Also, as noted by @АртёмЦарионов below, EPPlus has support for Pivot Tables and ExcelLibrary may have some support (Pivot table issue in ExcelLibrary)

Here are a couple links for quick reference:
ExcelLibrary – GNU Lesser GPL
EPPlus – GNU (LGPL) – No longer maintained
EPPlus 5 – Polyform Noncommercial – Starting May 2020
NPOI – Apache License

Here some example code for ExcelLibrary:

Here is an example taking data from a database and creating a workbook from it. Note that the ExcelLibrary code is the single line at the bottom:

//Create the data set and table
DataSet ds = new DataSet("New_DataSet");
DataTable dt = new DataTable("New_DataTable");

//Set the locale for each
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
dt.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;

//Open a DB connection (in this example with OleDB)
OleDbConnection con = new OleDbConnection(dbConnectionString);
con.Open();

//Create a query and fill the data table with the data from the DB
string sql = "SELECT Whatever FROM MyDBTable;";
OleDbCommand cmd = new OleDbCommand(sql, con);
OleDbDataAdapter adptr = new OleDbDataAdapter();

adptr.SelectCommand = cmd;
adptr.Fill(dt);
con.Close();

//Add the table to the data set
ds.Tables.Add(dt);

//Here's the easy part. Create the Excel worksheet from the data set
ExcelLibrary.DataSetHelper.CreateWorkbook("MyExcelFile.xls", ds);

Creating the Excel file is as easy as that. You can also manually create Excel files, but the above functionality is what really impressed me.

C# – Get int value from enum in C#

2601

Just cast the enum, e.g.

int something = (int) Question.Role;

The above will work for the vast majority of enums you see in the wild, as the default underlying type for an enum is int.

However, as cecilphillip points out, enums can have different underlying types. If an enum is declared as a uintlong, or ulong, it should be cast to the type of the enum; e.g. for

enum StarsInMilkyWay:long {Sun = 1, V645Centauri = 2 .. Wolf424B = 2147483649};

you should use

long something = (long)StarsInMilkyWay.Wolf424B;

C# – What is the best way to give a C# auto-property an initial value?

In C# 5 and earlier, to give auto implemented properties an initial value, you have to do it in a constructor.

Since C# 6.0, you can specify initial value in-line. The syntax is:

public int X { get; set; } = x; // C# 6 or higher

DefaultValueAttribute is intended to be used by the VS designer (or any other consumer) to specify a default value, not an initial value. (Even if in designed object, initial value is the default value).

At compile time DefaultValueAttribute will not impact the generated IL and it will not be read to initialize the property to that value (see DefaultValue attribute is not working with my Auto Property).

C# – How do I generate a random int number?

The Random class is used to create random numbers. (Pseudo-random that is of course.).

Example:

Random rnd = new Random();
int month  = rnd.Next(1, 13);  // creates a number between 1 and 12
int dice   = rnd.Next(1, 7);   // creates a number between 1 and 6
int card   = rnd.Next(52);     // creates a number between 0 and 51

If you are going to create more than one random number, you should keep the Random instance and reuse it. If you create new instances too close in time, they will produce the same series of random numbers as the random generator is seeded from the system clock.

C# – Should ‘using’ directives be inside or outside the namespace?

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there’s already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It’s also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

C# – How do I get a consistent byte representation of strings in C# without manually specifying an encoding?

Contrary to the answers here, you DON’T need to worry about encoding if the bytes don’t need to be interpreted!

Like you mentioned, your goal is, simply, to “get what bytes the string has been stored in”.
(And, of course, to be able to re-construct the string from the bytes.)

For those goals, I honestly do not understand why people keep telling you that you need the encodings. You certainly do NOT need to worry about encodings for this.

Just do this instead:

static byte[] GetBytes(string str)
{
    byte[] bytes = new byte[str.Length * sizeof(char)];
    System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
    return bytes;
}

// Do NOT use on arbitrary bytes; only use on GetBytes's output on the SAME system
static string GetString(byte[] bytes)
{
    char[] chars = new char[bytes.Length / sizeof(char)];
    System.Buffer.BlockCopy(bytes, 0, chars, 0, bytes.Length);
    return new string(chars);
}

As long as your program (or other programs) don’t try to interpret the bytes somehow, which you obviously didn’t mention you intend to do, then there is nothing wrong with this approach! Worrying about encodings just makes your life more complicated for no real reason.

Additional benefit to this approach: It doesn’t matter if the string contains invalid characters, because you can still get the data and reconstruct the original string anyway!

It will be encoded and decoded just the same, because you are just looking at the bytes.

If you used a specific encoding, though, it would’ve given you trouble with encoding/decoding invalid characters.

C# – Deep cloning objects

1807

Whereas one approach is to implement the ICloneable interface (described here, so I won’t regurgitate), here’s a nice deep clone object copier I found on The Code Project a while ago and incorporated it into our code. As mentioned elsewhere, it requires your objects to be serializable.

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

/// <summary>
/// Reference Article http://www.codeproject.com/KB/tips/SerializedObjectCloner.aspx
/// Provides a method for performing a deep copy of an object.
/// Binary Serialization is used to perform the copy.
/// </summary>
public static class ObjectCopier
{
    /// <summary>
    /// Perform a deep copy of the object via serialization.
    /// </summary>
    /// <typeparam name="T">The type of object being copied.</typeparam>
    /// <param name="source">The object instance to copy.</param>
    /// <returns>A deep copy of the object.</returns>
    public static T Clone<T>(T source)
    {
        if (!typeof(T).IsSerializable)
        {
            throw new ArgumentException("The type must be serializable.", nameof(source));
        }

        // Don't serialize a null object, simply return the default for that object
        if (ReferenceEquals(self, null)) return default;

        using var Stream stream = new MemoryStream();
        IFormatter formatter = new BinaryFormatter();
        formatter.Serialize(stream, source);
        stream.Seek(0, SeekOrigin.Begin);
        return (T)formatter.Deserialize(stream);
    }
}

The idea is that it serializes your object and then deserializes it into a fresh object. The benefit is that you don’t have to concern yourself about cloning everything when an object gets too complex.

In case of you prefer to use the new extension methods of C# 3.0, change the method to have the following signature:

public static T Clone<T>(this T source)
{
   // ...
}

Now the method call simply becomes objectBeingCloned.Clone();.

EDIT (January 10 2015) Thought I’d revisit this, to mention I recently started using (Newtonsoft) Json to do this, it should be lighter, and avoids the overhead of [Serializable] tags. (NB @atconway has pointed out in the comments that private members are not cloned using the JSON method)

/// <summary>
/// Perform a deep Copy of the object, using Json as a serialization method. NOTE: Private members are not cloned using this method.
/// </summary>
/// <typeparam name="T">The type of object being copied.</typeparam>
/// <param name="source">The object instance to copy.</param>
/// <returns>The copied object.</returns>
public static T CloneJson<T>(this T source)
{            
    // Don't serialize a null object, simply return the default for that object
    if (ReferenceEquals(self, null)) return default;

    // initialize inner objects individually
    // for example in default constructor some list property initialized with some values,
    // but in 'source' these items are cleaned -
    // without ObjectCreationHandling.Replace default constructor values will be added to result
    var deserializeSettings = new JsonSerializerSettings {ObjectCreationHandling = ObjectCreationHandling.Replace};

    return JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(source), deserializeSettings);
}

C# – What are the correct version numbers for C#?

C# language version history:

These are the versions of C# known about at the time of this writing:

C# – Case insensitive ‘Contains(string)’

To test if the string paragraph contains the string word (thanks @QuarterMeister)

culture.CompareInfo.IndexOf(paragraph, word, CompareOptions.IgnoreCase) >= 0

Where culture is the instance of CultureInfo describing the language that the text is written in.

This solution is transparent about the definition of case-insensitivity, which is language dependent. For example, the English language uses the characters I and i for the upper and lower case versions of the ninth letter, whereas the Turkish language uses these characters for the eleventh and twelfth letters of its 29 letter-long alphabet. The Turkish upper case version of ‘i’ is the unfamiliar character ‘İ’.

Thus the strings tin and TIN are the same word in English, but different words in Turkish. As I understand, one means ‘spirit’ and the other is an onomatopoeia word. (Turks, please correct me if I’m wrong, or suggest a better example)

To summarise, you can only answer the question ‘are these two strings the same but in different cases’ if you know what language the text is in. If you don’t know, you’ll have to take a punt. Given English’s hegemony in software, you should probably resort to CultureInfo.InvariantCulture, because it will be wrong in familiar ways.

C# – How can I cast int to enum?

4154

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

C# – What is the difference between String and string in C#?

string is an alias in C# for System.String.

So technically, there is no difference. It’s like int vs. System.Int32.

As far as guidelines, it’s generally recommended to use string any time you’re referring to an object.

e.g.

string place = "world";

Likewise, I think it’s generally recommended to use String if you need to refer specifically to the class.

e.g.

string greet = String.Format("Hello {0}!", place);

C# Multithreading

thread is defined as the execution path of a program. Each thread defines a unique flow of control. If your application involves complicated and time consuming operations, then it is often helpful to set different execution paths or threads, with each thread performing a particular job.

Threads are lightweight processes. One common example of use of thread is implementation of concurrent programming by modern operating systems. Use of threads saves wastage of CPU cycle and increase efficiency of an application.

So far we wrote the programs where a single thread runs as a single process which is the running instance of the application. However, this way the application can perform one job at a time. To make it execute more than one task at a time, it could be divided into smaller threads.

Thread Life Cycle

The life cycle of a thread starts when an object of the System.Threading.Thread class is created and ends when the thread is terminated or completes execution.

Following are the various states in the life cycle of a thread −

  • The Unstarted State − It is the situation when the instance of the thread is created but the Start method is not called.
  • The Ready State − It is the situation when the thread is ready to run and waiting CPU cycle.
  • The Not Runnable State − A thread is not executable, when
    • Sleep method has been called
    • Wait method has been called
    • Blocked by I/O operations
  • The Dead State − It is the situation when the thread completes execution or is aborted.

The Main Thread

In C#, the System.Threading.Thread class is used for working with threads. It allows creating and accessing individual threads in a multithreaded application. The first thread to be executed in a process is called the main thread.

When a C# program starts execution, the main thread is automatically created. The threads created using the Thread class are called the child threads of the main thread. You can access a thread using the CurrentThread property of the Thread class.

The following program demonstrates main thread execution −Live Demo

using System;
using System.Threading;

namespace MultithreadingApplication {
   class MainThreadProgram {
      static void Main(string[] args) {
         Thread th = Thread.CurrentThread;
         th.Name = "MainThread";
         
         Console.WriteLine("This is {0}", th.Name);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

This is MainThread

Properties and Methods of the Thread Class

The following table shows some most commonly used properties of the Thread class −

Sr.No.Property & Description
1CurrentContextGets the current context in which the thread is executing.
2CurrentCultureGets or sets the culture for the current thread.
3CurrentPrincipleGets or sets the thread’s current principal (for role-based security).
4CurrentThreadGets the currently running thread.
5CurrentUICultureGets or sets the current culture used by the Resource Manager to look up culture-specific resources at run-time.
6ExecutionContextGets an ExecutionContext object that contains information about the various contexts of the current thread.
7IsAliveGets a value indicating the execution status of the current thread.
8IsBackgroundGets or sets a value indicating whether or not a thread is a background thread.
9IsThreadPoolThreadGets a value indicating whether or not a thread belongs to the managed thread pool.
10ManagedThreadIdGets a unique identifier for the current managed thread.
11NameGets or sets the name of the thread.
12PriorityGets or sets a value indicating the scheduling priority of a thread.
13ThreadStateGets a value containing the states of the current thread.

The following table shows some of the most commonly used methods of the Thread class −

Sr.No.Method & Description
1public void Abort()Raises a ThreadAbortException in the thread on which it is invoked, to begin the process of terminating the thread. Calling this method usually terminates the thread.
2public static LocalDataStoreSlot AllocateDataSlot()Allocates an unnamed data slot on all the threads. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
3public static LocalDataStoreSlot AllocateNamedDataSlot(string name)Allocates a named data slot on all threads. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
4public static void BeginCriticalRegion()Notifies a host that execution is about to enter a region of code in which the effects of a thread abort or unhandled exception might jeopardize other tasks in the application domain.
5public static void BeginThreadAffinity()Notifies a host that managed code is about to execute instructions that depend on the identity of the current physical operating system thread.
6public static void EndCriticalRegion()Notifies a host that execution is about to enter a region of code in which the effects of a thread abort or unhandled exception are limited to the current task.
7public static void EndThreadAffinity()Notifies a host that managed code has finished executing instructions that depend on the identity of the current physical operating system thread.
8public static void FreeNamedDataSlot(string name)Eliminates the association between a name and a slot, for all threads in the process. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
9public static Object GetData(LocalDataStoreSlot slot)Retrieves the value from the specified slot on the current thread, within the current thread’s current domain. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
10public static AppDomain GetDomain()Returns the current domain in which the current thread is running.
11public static AppDomain GetDomainID()Returns a unique application domain identifier
12public static LocalDataStoreSlot GetNamedDataSlot(string name)Looks up a named data slot. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
13public void Interrupt()Interrupts a thread that is in the WaitSleepJoin thread state.
14public void Join()Blocks the calling thread until a thread terminates, while continuing to perform standard COM and SendMessage pumping. This method has different overloaded forms.
15public static void MemoryBarrier()Synchronizes memory access as follows: The processor executing the current thread cannot reorder instructions in such a way that memory accesses prior to the call to MemoryBarrier execute after memory accesses that follow the call to MemoryBarrier.
16public static void ResetAbort()Cancels an Abort requested for the current thread.
17public static void SetData(LocalDataStoreSlot slot, Object data)Sets the data in the specified slot on the currently running thread, for that thread’s current domain. For better performance, use fields marked with the ThreadStaticAttribute attribute instead.
18public void Start()Starts a thread.
19public static void Sleep(int millisecondsTimeout)Makes the thread pause for a period of time.
20public static void SpinWait(int iterations)Causes a thread to wait the number of times defined by the iterations parameter
21public static byte VolatileRead(ref byte address)public static double VolatileRead(ref double address)public static int VolatileRead(ref int address)public static Object VolatileRead(ref Object address)Reads the value of a field. The value is the latest written by any processor in a computer, regardless of the number of processors or the state of processor cache. This method has different overloaded forms. Only some are given above.
22public static void VolatileWrite(ref byte address,byte value)public static void VolatileWrite(ref double address, double value)public static void VolatileWrite(ref int address, int value)public static void VolatileWrite(ref Object address, Object value)Writes a value to a field immediately, so that the value is visible to all processors in the computer. This method has different overloaded forms. Only some are given above.
23public static bool Yield()Causes the calling thread to yield execution to another thread that is ready to run on the current processor. The operating system selects the thread to yield to.

Creating Threads

Threads are created by extending the Thread class. The extended Thread class then calls the Start() method to begin the child thread execution.

The following program demonstrates the concept −Live Demo

using System;
using System.Threading;

namespace MultithreadingApplication {
   class ThreadCreationProgram {
      public static void CallToChildThread() {
         Console.WriteLine("Child thread starts");
      }
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         Thread childThread = new Thread(childref);
         childThread.Start();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts

Managing Threads

The Thread class provides various methods for managing threads.

The following example demonstrates the use of the sleep() method for making a thread pause for a specific period of time.Live Demo

using System;
using System.Threading;

namespace MultithreadingApplication {
   class ThreadCreationProgram {
      public static void CallToChildThread() {
         Console.WriteLine("Child thread starts");
         
         // the thread is paused for 5000 milliseconds
         int sleepfor = 5000; 
         
         Console.WriteLine("Child Thread Paused for {0} seconds", sleepfor / 1000);
         Thread.Sleep(sleepfor);
         Console.WriteLine("Child thread resumes");
      }
      
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         
         Thread childThread = new Thread(childref);
         childThread.Start();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts
Child Thread Paused for 5 seconds
Child thread resumes

Destroying Threads

The Abort() method is used for destroying threads.

The runtime aborts the thread by throwing a ThreadAbortException. This exception cannot be caught, the control is sent to the finally block, if any.

The following program illustrates this −Live Demo

using System;
using System.Threading;

namespace MultithreadingApplication {
   class ThreadCreationProgram {
      public static void CallToChildThread() {
         try {
            Console.WriteLine("Child thread starts");
            
            // do some work, like counting to 10
            for (int counter = 0; counter <= 10; counter++) {
               Thread.Sleep(500);
               Console.WriteLine(counter);
            }
            
            Console.WriteLine("Child Thread Completed");
         } catch (ThreadAbortException e) {
            Console.WriteLine("Thread Abort Exception");
         } finally {
            Console.WriteLine("Couldn't catch the Thread Exception");
         }
      }
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         
         Thread childThread = new Thread(childref);
         childThread.Start();
         
         //stop the main thread for some time
         Thread.Sleep(2000);
         
         //now abort the child
         Console.WriteLine("In Main: Aborting the Child thread");
         
         childThread.Abort();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts
0
1
2
In Main: Aborting the Child thread
Thread Abort Exception
Couldn't catch the Thread Exception 

C# Unsafe Codes

C# allows using pointer variables in a function of code block when it is marked by the unsafe modifier. The unsafe code or the unmanaged code is a code block that uses a pointer variable.

Note − To execute the programs mentioned in this chapter at codingground, please set compilation option in Project >> Compile Options >> Compilation Command to

mcs *.cs -out:main.exe -unsafe"

Pointers

pointer is a variable whose value is the address of another variable i.e., the direct address of the memory location. similar to any variable or constant, you must declare a pointer before you can use it to store any variable address.

The general form of a pointer declaration is −

type *var-name;

Following are valid pointer declarations −

int    *ip;    /* pointer to an integer */
double *dp;    /* pointer to a double */
float  *fp;    /* pointer to a float */
char   *ch     /* pointer to a character */

The following example illustrates use of pointers in C#, using the unsafe modifier −

using System;

namespace UnsafeCodeApplication {
   class Program {
      static unsafe void Main(string[] args) {
         int var = 20;
         int* p = &var;
         
         Console.WriteLine("Data is: {0} ",  var);
         Console.WriteLine("Address is: {0}",  (int)p);
         Console.ReadKey();
      }
   }
}

When the above code wass compiled and executed, it produces the following result −

Data is: 20
Address is: 99215364

Instead of declaring an entire method as unsafe, you can also declare a part of the code as unsafe. The example in the following section shows this.

Retrieving the Data Value Using a Pointer

You can retrieve the data stored at the located referenced by the pointer variable, using the ToString() method. The following example demonstrates this −

using System;

namespace UnsafeCodeApplication {
   class Program {
      public static void Main() {
         unsafe {
            int var = 20;
            int* p = &var;
            
            Console.WriteLine("Data is: {0} " , var);
            Console.WriteLine("Data is: {0} " , p->ToString());
            Console.WriteLine("Address is: {0} " , (int)p);
         }
         Console.ReadKey();
      }
   }
}

When the above code was compiled and executed, it produces the following result −

Data is: 20
Data is: 20
Address is: 77128984

Passing Pointers as Parameters to Methods

You can pass a pointer variable to a method as parameter. The following example illustrates this −

using System;

namespace UnsafeCodeApplication {
   class TestPointer {
      public unsafe void swap(int* p, int *q) {
         int temp = *p;
         *p = *q;
         *q = temp;
      }
      public unsafe static void Main() {
         TestPointer p = new TestPointer();
         int var1 = 10;
         int var2 = 20;
         int* x = &var1;
         int* y = &var2;
         
         Console.WriteLine("Before Swap: var1:{0}, var2: {1}", var1, var2);
         p.swap(x, y);

         Console.WriteLine("After Swap: var1:{0}, var2: {1}", var1, var2);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Before Swap: var1: 10, var2: 20
After Swap: var1: 20, var2: 10

Accessing Array Elements Using a Pointer

In C#, an array name and a pointer to a data type same as the array data, are not the same variable type. For example, int *p and int[] p, are not same type. You can increment the pointer variable p because it is not fixed in memory but an array address is fixed in memory, and you can’t increment that.

Therefore, if you need to access an array data using a pointer variable, as we traditionally do in C, or C++ ( please check: C Pointers), you need to fix the pointer using the fixed keyword.

The following example demonstrates this −

using System;

namespace UnsafeCodeApplication {
   class TestPointer {
      public unsafe static void Main() {
         int[]  list = {10, 100, 200};
         fixed(int *ptr = list)
         
         /* let us have array address in pointer */
         for ( int i = 0; i < 3; i++) {
            Console.WriteLine("Address of list[{0}]={1}",i,(int)(ptr + i));
            Console.WriteLine("Value of list[{0}]={1}", i, *(ptr + i));
         }
         
         Console.ReadKey();
      }
   }
}

When the above code was compiled and executed, it produces the following result −

Address of list[0] = 31627168
Value of list[0] = 10
Address of list[1] = 31627172
Value of list[1] = 100
Address of list[2] = 31627176
Value of list[2] = 200

Compiling Unsafe Code

For compiling unsafe code, you have to specify the /unsafe command-line switch with command-line compiler.

For example, to compile a program named prog1.cs containing unsafe code, from command line, give the command −

csc /unsafe prog1.cs

If you are using Visual Studio IDE then you need to enable use of unsafe code in the project properties.

To do this −

  • Open project properties by double clicking the properties node in the Solution Explorer.
  • Click on the Build tab.
  • Select the option “Allow unsafe code“.

C# Anonymous Methods

We discussed that delegates are used to reference any methods that has the same signature as that of the delegate. In other words, you can call a method that can be referenced by a delegate using that delegate object.

Anonymous methods provide a technique to pass a code block as a delegate parameter. Anonymous methods are the methods without a name, just the body.

You need not specify the return type in an anonymous method; it is inferred from the return statement inside the method body.

Writing an Anonymous Method

Anonymous methods are declared with the creation of the delegate instance, with a delegate keyword. For example,

delegate void NumberChanger(int n);
...
NumberChanger nc = delegate(int x) {
   Console.WriteLine("Anonymous Method: {0}", x);
};

The code block Console.WriteLine(“Anonymous Method: {0}”, x); is the body of the anonymous method.

The delegate could be called both with anonymous methods as well as named methods in the same way, i.e., by passing the method parameters to the delegate object.

For example,

nc(10);

Example

The following example demonstrates the concept −Live Demo

using System;

delegate void NumberChanger(int n);
namespace DelegateAppl {
   class TestDelegate {
      static int num = 10;
      
      public static void AddNum(int p) {
         num += p;
         Console.WriteLine("Named Method: {0}", num);
      }
      public static void MultNum(int q) {
         num *= q;
         Console.WriteLine("Named Method: {0}", num);
      }
      public static int getNum() {
         return num;
      }
      static void Main(string[] args) {
         //create delegate instances using anonymous method
         NumberChanger nc = delegate(int x) {
            Console.WriteLine("Anonymous Method: {0}", x);
         };
         
         //calling the delegate using the anonymous method 
         nc(10);
         
         //instantiating the delegate using the named methods 
         nc =  new NumberChanger(AddNum);
         
         //calling the delegate using the named methods 
         nc(5);
         
         //instantiating the delegate using another named methods 
         nc =  new NumberChanger(MultNum);
         
         //calling the delegate using the named methods 
         nc(2);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Anonymous Method: 10
Named Method: 15
Named Method: 30

C# Generics

Generics allow you to define the specification of the data type of programming elements in a class or a method, until it is actually used in the program. In other words, generics allow you to write a class or method that can work with any data type.

You write the specifications for the class or the method, with substitute parameters for data types. When the compiler encounters a constructor for the class or a function call for the method, it generates code to handle the specific data type. A simple example would help understanding the concept −Live Demo

using System;
using System.Collections.Generic;

namespace GenericApplication {
   public class MyGenericArray<T> {
      private T[] array;
      
      public MyGenericArray(int size) {
         array = new T[size + 1];
      }
      public T getItem(int index) {
         return array[index];
      }
      public void setItem(int index, T value) {
         array[index] = value;
      }
   }
   class Tester {
      static void Main(string[] args) {
         
         //declaring an int array
         MyGenericArray<int> intArray = new MyGenericArray<int>(5);
         
         //setting values
         for (int c = 0; c < 5; c++) {
            intArray.setItem(c, c*5);
         }
         
         //retrieving the values
         for (int c = 0; c < 5; c++) {
            Console.Write(intArray.getItem(c) + " ");
         }
         
         Console.WriteLine();
         
         //declaring a character array
         MyGenericArray<char> charArray = new MyGenericArray<char>(5);
         
         //setting values
         for (int c = 0; c < 5; c++) {
            charArray.setItem(c, (char)(c+97));
         }
         
         //retrieving the values
         for (int c = 0; c< 5; c++) {
            Console.Write(charArray.getItem(c) + " ");
         }
         Console.WriteLine();
         
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

0 5 10 15 20
a b c d e

Features of Generics

Generics is a technique that enriches your programs in the following ways −

  • It helps you to maximize code reuse, type safety, and performance.
  • You can create generic collection classes. The .NET Framework class library contains several new generic collection classes in the System.Collections.Generic namespace. You may use these generic collection classes instead of the collection classes in the System.Collections namespace.
  • You can create your own generic interfaces, classes, methods, events, and delegates.
  • You may create generic classes constrained to enable access to methods on particular data types.
  • You may get information on the types used in a generic data type at run-time by means of reflection.

Generic Methods

In the previous example, we have used a generic class; we can declare a generic method with a type parameter. The following program illustrates the concept −Live Demo

using System;
using System.Collections.Generic;

namespace GenericMethodAppl {
   class Program {
      static void Swap<T>(ref T lhs, ref T rhs) {
         T temp;
         temp = lhs;
         lhs = rhs;
         rhs = temp;
      }
      static void Main(string[] args) {
         int a, b;
         char c, d;
         a = 10;
         b = 20;
         c = 'I';
         d = 'V';
         
         //display values before swap:
         Console.WriteLine("Int values before calling swap:");
         Console.WriteLine("a = {0}, b = {1}", a, b);
         Console.WriteLine("Char values before calling swap:");
         Console.WriteLine("c = {0}, d = {1}", c, d);
         
         //call swap
         Swap<int>(ref a, ref b);
         Swap<char>(ref c, ref d);
         
         //display values after swap:
         Console.WriteLine("Int values after calling swap:");
         Console.WriteLine("a = {0}, b = {1}", a, b);
         Console.WriteLine("Char values after calling swap:");
         Console.WriteLine("c = {0}, d = {1}", c, d);
         
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Int values before calling swap:
a = 10, b = 20
Char values before calling swap:
c = I, d = V
Int values after calling swap:
a = 20, b = 10
Char values after calling swap:
c = V, d = I

Generic Delegates

You can define a generic delegate with type parameters. For example −

delegate T NumberChanger<T>(T n);

The following example shows use of this delegate −Live Demo

using System;
using System.Collections.Generic;

delegate T NumberChanger<T>(T n);
namespace GenericDelegateAppl {
   class TestDelegate {
      static int num = 10;
      
      public static int AddNum(int p) {
         num += p;
         return num;
      }
      public static int MultNum(int q) {
         num *= q;
         return num;
      }
      public static int getNum() {
         return num;
      }
      static void Main(string[] args) {
         //create delegate instances
         NumberChanger<int> nc1 = new NumberChanger<int>(AddNum);
         NumberChanger<int> nc2 = new NumberChanger<int>(MultNum);
         
         //calling the methods using the delegate objects
         nc1(25);
         Console.WriteLine("Value of Num: {0}", getNum());
         
         nc2(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of Num: 35
Value of Num: 175

C# Collections

Collection classes are specialized classes for data storage and retrieval. These classes provide support for stacks, queues, lists, and hash tables. Most collection classes implement the same interfaces.

Collection classes serve various purposes, such as allocating memory dynamically to elements and accessing a list of items on the basis of an index etc. These classes create collections of objects of the Object class, which is the base class for all data types in C#.

Various Collection Classes and Their Usage

The following are the various commonly used classes of the System.Collection namespace. Click the following links to check their detail.

Sr.No.Class & Description and Useage
1ArrayListIt represents ordered collection of an object that can be indexed individually.It is basically an alternative to an array. However, unlike array you can add and remove items from a list at a specified position using an index and the array resizes itself automatically. It also allows dynamic memory allocation, adding, searching and sorting items in the list.
2HashtableIt uses a key to access the elements in the collection.A hash table is used when you need to access elements by using key, and you can identify a useful key value. Each item in the hash table has a key/value pair. The key is used to access the items in the collection.
3SortedListIt uses a key as well as an index to access the items in a list.A sorted list is a combination of an array and a hash table. It contains a list of items that can be accessed using a key or an index. If you access items using an index, it is an ArrayList, and if you access items using a key , it is a Hashtable. The collection of items is always sorted by the key value.
4StackIt represents a last-in, first out collection of object.It is used when you need a last-in, first-out access of items. When you add an item in the list, it is called pushing the item and when you remove it, it is called popping the item.
5QueueIt represents a first-in, first out collection of object.It is used when you need a first-in, first-out access of items. When you add an item in the list, it is called enqueue and when you remove an item, it is called deque.
6BitArrayIt represents an array of the binary representation using the values 1 and 0.It is used when you need to store the bits but do not know the number of bits in advance. You can access items from the BitArray collection by using an integer index, which starts from zero.

C# Events

Events are user actions such as key press, clicks, mouse movements, etc., or some occurrence such as system generated notifications. Applications need to respond to events when they occur. For example, interrupts. Events are used for inter-process communication.

Using Delegates with Events

The events are declared and raised in a class and associated with the event handlers using delegates within the same class or some other class. The class containing the event is used to publish the event. This is called the publisher class. Some other class that accepts this event is called the subscriber class. Events use the publisher-subscriber model.

publisher is an object that contains the definition of the event and the delegate. The event-delegate association is also defined in this object. A publisher class object invokes the event and it is notified to other objects.

subscriber is an object that accepts the event and provides an event handler. The delegate in the publisher class invokes the method (event handler) of the subscriber class.

Declaring Events

To declare an event inside a class, first of all, you must declare a delegate type for the even as:

public delegate string BoilerLogHandler(string str);

then, declare the event using the event keyword −

event BoilerLogHandler BoilerEventLog;

The preceding code defines a delegate named BoilerLogHandler and an event named BoilerEventLog, which invokes the delegate when it is raised.

C# Delegates

C# delegates are similar to pointers to functions, in C or C++. A delegate is a reference type variable that holds the reference to a method. The reference can be changed at runtime.

Delegates are especially used for implementing events and the call-back methods. All delegates are implicitly derived from the System.Delegate class.

Declaring Delegates

Delegate declaration determines the methods that can be referenced by the delegate. A delegate can refer to a method, which has the same signature as that of the delegate.

For example, consider a delegate −

public delegate int MyDelegate (string s);

The preceding delegate can be used to reference any method that has a single string parameter and returns an int type variable.

Syntax for delegate declaration is −

delegate <return type> <delegate-name> <parameter list>

Instantiating Delegates

Once a delegate type is declared, a delegate object must be created with the new keyword and be associated with a particular method. When creating a delegate, the argument passed to the new expression is written similar to a method call, but without the arguments to the method. For example −

public delegate void printString(string s);
...
printString ps1 = new printString(WriteToScreen);
printString ps2 = new printString(WriteToFile);

Following example demonstrates declaration, instantiation, and use of a delegate that can be used to reference methods that take an integer parameter and returns an integer value.Live Demo

using System;

delegate int NumberChanger(int n);
namespace DelegateAppl {
   
   class TestDelegate {
      static int num = 10;
      
      public static int AddNum(int p) {
         num += p;
         return num;
      }
      public static int MultNum(int q) {
         num *= q;
         return num;
      }
      public static int getNum() {
         return num;
      }
      static void Main(string[] args) {
         //create delegate instances
         NumberChanger nc1 = new NumberChanger(AddNum);
         NumberChanger nc2 = new NumberChanger(MultNum);
         
         //calling the methods using the delegate objects
         nc1(25);
         Console.WriteLine("Value of Num: {0}", getNum());
         nc2(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of Num: 35
Value of Num: 175

Multicasting of a Delegate

Delegate objects can be composed using the “+” operator. A composed delegate calls the two delegates it was composed from. Only delegates of the same type can be composed. The “-” operator can be used to remove a component delegate from a composed delegate.

Using this property of delegates you can create an invocation list of methods that will be called when a delegate is invoked. This is called multicasting of a delegate. The following program demonstrates multicasting of a delegate −Live Demo

using System;

delegate int NumberChanger(int n);
namespace DelegateAppl {
   class TestDelegate {
      static int num = 10;
      
      public static int AddNum(int p) {
         num += p;
         return num;
      }
      public static int MultNum(int q) {
         num *= q;
         return num;
      }
      public static int getNum() {
         return num;
      }
      static void Main(string[] args) {
         //create delegate instances
         NumberChanger nc;
         NumberChanger nc1 = new NumberChanger(AddNum);
         NumberChanger nc2 = new NumberChanger(MultNum);
         
         nc = nc1;
         nc += nc2;
         
         //calling multicast
         nc(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of Num: 75

Using Delegates

The following example demonstrates the use of delegate. The delegate printString can be used to reference method that takes a string as input and returns nothing.

We use this delegate to call two methods, the first prints the string to the console, and the second one prints it to a file −Live Demo

using System;
using System.IO;

namespace DelegateAppl {

   class PrintString {
      static FileStream fs;
      static StreamWriter sw;
      
      // delegate declaration
      public delegate void printString(string s);

      // this method prints to the console
      public static void WriteToScreen(string str) {
         Console.WriteLine("The String is: {0}", str);
      }
      
      //this method prints to a file
      public static void WriteToFile(string s) {
         fs = new FileStream("c:\\message.txt",
         FileMode.Append, FileAccess.Write);
         sw = new StreamWriter(fs);
         sw.WriteLine(s);
         sw.Flush();
         sw.Close();
         fs.Close();
      }
      
      // this method takes the delegate as parameter and uses it to
      // call the methods as required
      public static void sendString(printString ps) {
         ps("Hello World");
      }
      
      static void Main(string[] args) {
         printString ps1 = new printString(WriteToScreen);
         printString ps2 = new printString(WriteToFile);
         sendString(ps1);
         sendString(ps2);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

The String is: Hello World

C# Indexers

An indexer allows an object to be indexed such as an array. When you define an indexer for a class, this class behaves similar to a virtual array. You can then access the instance of this class using the array access operator ([ ]).

Syntax

A one dimensional indexer has the following syntax −

element-type this[int index] {

   // The get accessor.
   get {
      // return the value specified by index
   }
   
   // The set accessor.
   set {
      // set the value specified by index
   }
}

Use of Indexers

Declaration of behavior of an indexer is to some extent similar to a property. similar to the properties, you use get and set accessors for defining an indexer. However, properties return or set a specific data member, whereas indexers returns or sets a particular value from the object instance. In other words, it breaks the instance data into smaller parts and indexes each part, gets or sets each part.

Defining a property involves providing a property name. Indexers are not defined with names, but with the this keyword, which refers to the object instance. The following example demonstrates the concept −Live Demo

using System;

namespace IndexerApplication {
   
   class IndexedNames {
      private string[] namelist = new string[size];
      static public int size = 10;
      
      public IndexedNames() {
         for (int i = 0; i < size; i++)
         namelist[i] = "N. A.";
      }
      public string this[int index] {
         get {
            string tmp;
         
            if( index >= 0 && index <= size-1 ) {
               tmp = namelist[index];
            } else {
               tmp = "";
            }
            
            return ( tmp );
         }
         set {
            if( index >= 0 && index <= size-1 ) {
               namelist[index] = value;
            }
         }
      }
      static void Main(string[] args) {
         IndexedNames names = new IndexedNames();
         names[0] = "Zara";
         names[1] = "Riz";
         names[2] = "Nuha";
         names[3] = "Asif";
         names[4] = "Davinder";
         names[5] = "Sunil";
         names[6] = "Rubic";
         
         for ( int i = 0; i < IndexedNames.size; i++ ) {
            Console.WriteLine(names[i]);
         }
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Zara
Riz
Nuha
Asif
Davinder
Sunil
Rubic
N. A.
N. A.
N. A.

Overloaded Indexers

Indexers can be overloaded. Indexers can also be declared with multiple parameters and each parameter may be a different type. It is not necessary that the indexes have to be integers. C# allows indexes to be of other types, for example, a string.

The following example demonstrates overloaded indexers −Live Demo

using System;

namespace IndexerApplication {
   class IndexedNames {
      private string[] namelist = new string[size];
      static public int size = 10;
      
      public IndexedNames() {
         for (int i = 0; i < size; i++) {
            namelist[i] = "N. A.";
         }
      }
      public string this[int index] {
         get {
            string tmp;
            
            if( index >= 0 && index <= size-1 ) {
               tmp = namelist[index];
            } else {
               tmp = "";
            }
            
            return ( tmp );
         }
         set {
            if( index >= 0 && index <= size-1 ) {
               namelist[index] = value;
            }
         }
      }
      
      public int this[string name] {
         get {
            int index = 0;
            
            while(index < size) {
               if (namelist[index] == name) {
                return index;
               }
               index++;
            }
            return index;
         }
      }

      static void Main(string[] args) {
         IndexedNames names = new IndexedNames();
         names[0] = "Zara";
         names[1] = "Riz";
         names[2] = "Nuha";
         names[3] = "Asif";
         names[4] = "Davinder";
         names[5] = "Sunil";
         names[6] = "Rubic";
         
         //using the first indexer with int parameter
         for (int i = 0; i < IndexedNames.size; i++) {
            Console.WriteLine(names[i]);
         }
         
         //using the second indexer with the string parameter
         Console.WriteLine(names["Nuha"]);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Zara
Riz
Nuha
Asif
Davinder
Sunil
Rubic
N. A.
N. A.
N. A.
2

C# Properties

Properties are named members of classes, structures, and interfaces. Member variables or methods in a class or structures are called Fields. Properties are an extension of fields and are accessed using the same syntax. They use accessors through which the values of the private fields can be read, written or manipulated.

Properties do not name the storage locations. Instead, they have accessors that read, write, or compute their values.

For example, let us have a class named Student, with private fields for age, name, and code. We cannot directly access these fields from outside the class scope, but we can have properties for accessing these private fields.

Accessors

The accessor of a property contains the executable statements that helps in getting (reading or computing) or setting (writing) the property. The accessor declarations can contain a get accessor, a set accessor, or both. For example −

// Declare a Code property of type string:
public string Code {
   get {
      return code;
   }
   set {
      code = value;
   }
}

// Declare a Name property of type string:
public string Name {
   get {
      return name;
   }
   set {
      name = value;
   }
}

// Declare a Age property of type int:
public int Age { 
   get {
      return age;
   }
   set {
      age = value;
   }
}

Example

The following example demonstrates use of properties −Live Demo

using System;
namespace tutorialspoint {
   class Student {
      private string code = "N.A";
      private string name = "not known";
      private int age = 0;
      
      // Declare a Code property of type string:
      public string Code {
         get {
            return code;
         }
         set {
            code = value;
         }
      }
      
      // Declare a Name property of type string:
      public string Name {
         get {
            return name;
         }
         set {
            name = value;
         }
      }
      
      // Declare a Age property of type int:
      public int Age {
         get {
            return age;
         }
         set {
            age = value;
         }
      }
      public override string ToString() {
         return "Code = " + Code +", Name = " + Name + ", Age = " + Age;
      }
   }
   
   class ExampleDemo {
      public static void Main() {
      
         // Create a new Student object:
         Student s = new Student();
         
         // Setting code, name and the age of the student
         s.Code = "001";
         s.Name = "Zara";
         s.Age = 9;
         Console.WriteLine("Student Info: {0}", s);
         
         //let us increase age
         s.Age += 1;
         Console.WriteLine("Student Info: {0}", s);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Student Info: Code = 001, Name = Zara, Age = 9
Student Info: Code = 001, Name = Zara, Age = 10

Abstract Properties

An abstract class may have an abstract property, which should be implemented in the derived class. The following program illustrates this −Live Demo

using System;

namespace tutorialspoint {
   public abstract class Person {
      public abstract string Name {
         get;
         set;
      }
      public abstract int Age {
         get;
         set;
      }
   }
   class Student : Person {
      private string code = "N.A";
      private string name = "N.A";
      private int age = 0;
      
      // Declare a Code property of type string:
      public string Code {
         get {
            return code;
         }
         set {
            code = value;
         }
      }
      
      // Declare a Name property of type string:
      public override string Name {
         get {
            return name;
         }
         set {
            name = value;
         }
      }
      
      // Declare a Age property of type int:
      public override int Age {
         get {
            return age;
         }
         set {
            age = value;
         }
      }
      public override string ToString() {
         return "Code = " + Code +", Name = " + Name + ", Age = " + Age;
      }
   }
   
   class ExampleDemo {
      public static void Main() {
         // Create a new Student object:
         Student s = new Student();
         
         // Setting code, name and the age of the student
         s.Code = "001";
         s.Name = "Zara";
         s.Age = 9;
         Console.WriteLine("Student Info:- {0}", s);
         
         //let us increase age
         s.Age += 1;
         Console.WriteLine("Student Info:- {0}", s);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Student Info: Code = 001, Name = Zara, Age = 9
Student Info: Code = 001, Name = Zara, Age = 10

C# Reflection

Reflection objects are used for obtaining type information at runtime. The classes that give access to the metadata of a running program are in the System.Reflection namespace.

The System.Reflection namespace contains classes that allow you to obtain information about the application and to dynamically add types, values, and objects to the application.

Applications of Reflection

Reflection has the following applications −

  • It allows view attribute information at runtime.
  • It allows examining various types in an assembly and instantiate these types.
  • It allows late binding to methods and properties
  • It allows creating new types at runtime and then performs some tasks using those types.

Viewing Metadata

We have mentioned in the preceding chapter that using reflection you can view the attribute information.

The MemberInfo object of the System.Reflection class needs to be initialized for discovering the attributes associated with a class. To do this, you define an object of the target class, as −

System.Reflection.MemberInfo info = typeof(MyClass);

The following program demonstrates this −

using System;

[AttributeUsage(AttributeTargets.All)]
public class HelpAttribute : System.Attribute {
   public readonly string Url;
   
   public string Topic   // Topic is a named parameter {
      get {
         return topic;
      }
      set {
         topic = value;
      }
   }
   public HelpAttribute(string url)   // url is a positional parameter {
      this.Url = url;
   }
   private string topic;
}

[HelpAttribute("Information on the class MyClass")]
class MyClass {

}

namespace AttributeAppl {
   class Program {
      static void Main(string[] args) {
         System.Reflection.MemberInfo info = typeof(MyClass);
         object[] attributes = info.GetCustomAttributes(true);
         
         for (int i = 0; i < attributes.Length; i++) {
            System.Console.WriteLine(attributes[i]);
         }
         Console.ReadKey();
      }
   }
}

When it is compiled and run, it displays the name of the custom attributes attached to the class MyClass −

HelpAttribute

Example

In this example, we use the DeBugInfo attribute created in the previous chapter and use reflection to read metadata in the Rectangle class.Live Demo

using System;
using System.Reflection;

namespace BugFixApplication {
   //a custom attribute BugFix to be assigned to a class and its members
   [AttributeUsage(
      AttributeTargets.Class |
      AttributeTargets.Constructor |
      AttributeTargets.Field |
      AttributeTargets.Method |
      AttributeTargets.Property,
      AllowMultiple = true)]

   public class DeBugInfo : System.Attribute {
      private int bugNo;
      private string developer;
      private string lastReview;
      public string message;
      
      public DeBugInfo(int bg, string dev, string d) {
         this.bugNo = bg;
         this.developer = dev;
         this.lastReview = d;
      }
      public int BugNo {
         get {
            return bugNo;
         }
      }
      public string Developer {
         get {
            return developer;
         }
      }
      public string LastReview {
         get {
            return lastReview;
         }
      }
      public string Message {
         get {
            return message;
         }
         set {
            message = value;
         }
      }
   }
   [DeBugInfo(45, "Zara Ali", "12/8/2012", Message = "Return type mismatch")]
   [DeBugInfo(49, "Nuha Ali", "10/10/2012", Message = "Unused variable")]
   
   class Rectangle {
      //member variables
      protected double length;
      protected double width;
      
      public Rectangle(double l, double w) {
         length = l;
         width = w;
      }
      [DeBugInfo(55, "Zara Ali", "19/10/2012", Message = "Return type mismatch")]
      public double GetArea() {
         return length * width;
      }
      [DeBugInfo(56, "Zara Ali", "19/10/2012")]
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle(4.5, 7.5);
         r.Display();
         Type type = typeof(Rectangle);
         
         //iterating through the attribtues of the Rectangle class
         foreach (Object attributes in type.GetCustomAttributes(false)) {
            DeBugInfo dbi = (DeBugInfo)attributes;
            
            if (null != dbi) {
               Console.WriteLine("Bug no: {0}", dbi.BugNo);
               Console.WriteLine("Developer: {0}", dbi.Developer);
               Console.WriteLine("Last Reviewed: {0}", dbi.LastReview);
               Console.WriteLine("Remarks: {0}", dbi.Message);
            }
         }
         
         //iterating through the method attribtues
         foreach (MethodInfo m in type.GetMethods()) {
            
            foreach (Attribute a in m.GetCustomAttributes(true)) {
               DeBugInfo dbi = (DeBugInfo)a;
               
               if (null != dbi) {
                  Console.WriteLine("Bug no: {0}, for Method: {1}", dbi.BugNo, m.Name);
                  Console.WriteLine("Developer: {0}", dbi.Developer);
                  Console.WriteLine("Last Reviewed: {0}", dbi.LastReview);
                  Console.WriteLine("Remarks: {0}", dbi.Message);
               }
            }
         }
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 7.5
Area: 33.75
Bug No: 49
Developer: Nuha Ali
Last Reviewed: 10/10/2012
Remarks: Unused variable
Bug No: 45
Developer: Zara Ali
Last Reviewed: 12/8/2012
Remarks: Return type mismatch
Bug No: 55, for Method: GetArea
Developer: Zara Ali
Last Reviewed: 19/10/2012
Remarks: Return type mismatch
Bug No: 56, for Method: Display
Developer: Zara Ali
Last Reviewed: 19/10/2012
Remarks: 

C# Attributes

An attribute is a declarative tag that is used to convey information to runtime about the behaviors of various elements like classes, methods, structures, enumerators, assemblies etc. in your program. You can add declarative information to a program by using an attribute. A declarative tag is depicted by square ([ ]) brackets placed above the element it is used for.

Attributes are used for adding metadata, such as compiler instruction and other information such as comments, description, methods and classes to a program. The .Net Framework provides two types of attributes: the pre-defined attributes and custom built attributes.

Specifying an Attribute

Syntax for specifying an attribute is as follows −

[attribute(positional_parameters, name_parameter = value, ...)]
element

Name of the attribute and its values are specified within the square brackets, before the element to which the attribute is applied. Positional parameters specify the essential information and the name parameters specify the optional information.

Predefined Attributes

The .Net Framework provides three pre-defined attributes −

  • AttributeUsage
  • Conditional
  • Obsolete

AttributeUsage

The pre-defined attribute AttributeUsage describes how a custom attribute class can be used. It specifies the types of items to which the attribute can be applied.

Syntax for specifying this attribute is as follows −

[AttributeUsage (
   validon,
   AllowMultiple = allowmultiple,
   Inherited = inherited
)]

Where,

  • The parameter validon specifies the language elements on which the attribute can be placed. It is a combination of the value of an enumerator AttributeTargets. The default value is AttributeTargets.All.
  • The parameter allowmultiple (optional) provides value for the AllowMultiple property of this attribute, a Boolean value. If this is true, the attribute is multiuse. The default is false (single-use).
  • The parameter inherited (optional) provides value for the Inherited property of this attribute, a Boolean value. If it is true, the attribute is inherited by derived classes. The default value is false (not inherited).

For example,

[AttributeUsage(
   AttributeTargets.Class |
   AttributeTargets.Constructor |
   AttributeTargets.Field |
   AttributeTargets.Method |
   AttributeTargets.Property, 
   AllowMultiple = true)]

Conditional

This predefined attribute marks a conditional method whose execution depends on a specified preprocessing identifier.

It causes conditional compilation of method calls, depending on the specified value such as Debug or Trace. For example, it displays the values of the variables while debugging a code.

Syntax for specifying this attribute is as follows −

[Conditional(
   conditionalSymbol
)]

For example,

[Conditional("DEBUG")]

The following example demonstrates the attribute −Live Demo

#define DEBUG
using System;
using System.Diagnostics;

public class Myclass {
   [Conditional("DEBUG")]
   
   public static void Message(string msg) {
      Console.WriteLine(msg);
   }
}
class Test {
   static void function1() {
      Myclass.Message("In Function 1.");
      function2();
   }
   static void function2() {
      Myclass.Message("In Function 2.");
   }
   public static void Main() {
      Myclass.Message("In Main function.");
      function1();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

In Main function
In Function 1
In Function 2

Obsolete

This predefined attribute marks a program entity that should not be used. It enables you to inform the compiler to discard a particular target element. For example, when a new method is being used in a class and if you still want to retain the old method in the class, you may mark it as obsolete by displaying a message the new method should be used, instead of the old method.

Syntax for specifying this attribute is as follows −

[Obsolete (
   message
)]

[Obsolete (
   message,
   iserror
)]

Where,

  • The parameter message, is a string describing the reason why the item is obsolete and what to use instead.
  • The parameter iserror, is a Boolean value. If its value is true, the compiler should treat the use of the item as an error. Default value is false (compiler generates a warning).

The following program demonstrates this −

using System;

public class MyClass {
   [Obsolete("Don't use OldMethod, use NewMethod instead", true)]
   
   static void OldMethod() {
      Console.WriteLine("It is the old method");
   }
   static void NewMethod() {
      Console.WriteLine("It is the new method"); 
   }
   public static void Main() {
      OldMethod();
   }
}

When you try to compile the program, the compiler gives an error message stating −

 Don't use OldMethod, use NewMethod instead

Creating Custom Attributes

The .Net Framework allows creation of custom attributes that can be used to store declarative information and can be retrieved at run-time. This information can be related to any target element depending upon the design criteria and application need.

Creating and using custom attributes involve four steps −

  • Declaring a custom attribute
  • Constructing the custom attribute
  • Apply the custom attribute on a target program element
  • Accessing Attributes Through Reflection

The Last step involves writing a simple program to read through the metadata to find various notations. Metadata is data about data or information used for describing other data. This program should use reflections for accessing attributes at runtime. This we will discuss in the next chapter.

Declaring a Custom Attribute

A new custom attribute should is derived from the System.Attribute class. For example,

//a custom attribute BugFix to be assigned to a class and its members
[AttributeUsage(
   AttributeTargets.Class |
   AttributeTargets.Constructor |
   AttributeTargets.Field |
   AttributeTargets.Method |
   AttributeTargets.Property,
   AllowMultiple = true)]

public class DeBugInfo : System.Attribute

In the preceding code, we have declared a custom attribute named DeBugInfo.

Constructing the Custom Attribute

Let us construct a custom attribute named DeBugInfo, which stores the information obtained by debugging any program. Let it store the following information −

  • The code number for the bug
  • Name of the developer who identified the bug
  • Date of last review of the code
  • A string message for storing the developer’s remarks

The DeBugInfo class has three private properties for storing the first three information and a public property for storing the message. Hence the bug number, developer’s name, and date of review are the positional parameters of the DeBugInfo class and the message is an optional or named parameter.

Each attribute must have at least one constructor. The positional parameters should be passed through the constructor. The following code shows the DeBugInfo class −

//a custom attribute BugFix to be assigned to a class and its members
[AttributeUsage(
   AttributeTargets.Class |
   AttributeTargets.Constructor |
   AttributeTargets.Field |
   AttributeTargets.Method |
   AttributeTargets.Property,
   AllowMultiple = true)]

public class DeBugInfo : System.Attribute {
   private int bugNo;
   private string developer;
   private string lastReview;
   public string message;
   
   public DeBugInfo(int bg, string dev, string d) {
      this.bugNo = bg;
      this.developer = dev;
      this.lastReview = d;
   }
   public int BugNo {
      get {
         return bugNo;
      }
   }
   public string Developer {
      get {
         return developer;
      }
   }
   public string LastReview {
      get {
         return lastReview;
      }
   }
   public string Message {
      get {
         return message;
      }
      set {
         message = value;
      }
   }
}

Applying the Custom Attribute

The attribute is applied by placing it immediately before its target −

[DeBugInfo(45, "Zara Ali", "12/8/2012", Message = "Return type mismatch")]
[DeBugInfo(49, "Nuha Ali", "10/10/2012", Message = "Unused variable")]
class Rectangle {
   //member variables
   protected double length;
   protected double width;
   public Rectangle(double l, double w) {
      length = l;
      width = w;
   }
   [DeBugInfo(55, "Zara Ali", "19/10/2012", Message = "Return type mismatch")]
   
   public double GetArea() {
      return length * width;
   }
   [DeBugInfo(56, "Zara Ali", "19/10/2012")]
   
   public void Display() {
      Console.WriteLine("Length: {0}", length);
      Console.WriteLine("Width: {0}", width);
      Console.WriteLine("Area: {0}", GetArea());
   }
}

C# File Input Output

file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream.

The stream is basically the sequence of bytes passing through the communication path. There are two main streams: the input stream and the output stream. The input stream is used for reading data from file (read operation) and the output stream is used for writing into the file (write operation).

C# I/O Classes

The System.IO namespace has various classes that are used for performing numerous operations with files, such as creating and deleting files, reading from or writing to a file, closing a file etc.

The following table shows some commonly used non-abstract classes in the System.IO namespace −

Sr.No.I/O Class & Description
1BinaryReaderReads primitive data from a binary stream.
2BinaryWriterWrites primitive data in binary format.
3BufferedStreamA temporary storage for a stream of bytes.
4DirectoryHelps in manipulating a directory structure.
5DirectoryInfoUsed for performing operations on directories.
6DriveInfoProvides information for the drives.
7FileHelps in manipulating files.
8FileInfoUsed for performing operations on files.
9FileStreamUsed to read from and write to any location in a file.
10MemoryStreamUsed for random access to streamed data stored in memory.
11PathPerforms operations on path information.
12StreamReaderUsed for reading characters from a byte stream.
13StreamWriterIs used for writing characters to a stream.
14StringReaderIs used for reading from a string buffer.
15StringWriterIs used for writing into a string buffer.

The FileStream Class

The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream.

You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows −

FileStream <object_name> = new FileStream( <file_name>, <FileMode Enumerator>,
   <FileAccess Enumerator>, <FileShare Enumerator>);

For example, we create a FileStream object F for reading a file named sample.txt as shown −

FileStream F = new FileStream("sample.txt", FileMode.Open, FileAccess.Read,
   FileShare.Read);
Sr.No.Parameter & Description
1FileModeThe FileMode enumerator defines various methods for opening files. The members of the FileMode enumerator are −Append − It opens an existing file and puts cursor at the end of file, or creates the file, if the file does not exist.Create − It creates a new file.CreateNew − It specifies to the operating system, that it should create a new file.Open − It opens an existing file.OpenOrCreate − It specifies to the operating system that it should open a file if it exists, otherwise it should create a new file.Truncate − It opens an existing file and truncates its size to zero bytes.
2FileAccessFileAccess enumerators have members: ReadReadWrite and Write.
3FileShareFileShare enumerators have the following members −Inheritable − It allows a file handle to pass inheritance to the child processesNone − It declines sharing of the current fileRead − It allows opening the file for readin.ReadWrite − It allows opening the file for reading and writingWrite − It allows opening the file for writing

Example

The following program demonstrates use of the FileStream class −Live Demo

using System;
using System.IO;

namespace FileIOApplication {
   class Program {
      static void Main(string[] args) {
         FileStream F = new FileStream("test.dat", FileMode.OpenOrCreate, 
            FileAccess.ReadWrite);
         
         for (int i = 1; i <= 20; i++) {
            F.WriteByte((byte)i);
         }
         F.Position = 0;
         for (int i = 0; i <= 20; i++) {
            Console.Write(F.ReadByte() + " ");
         }
         F.Close();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1

Advanced File Operations in C#

The preceding example provides simple file operations in C#. However, to utilize the immense powers of C# System.IO classes, you need to know the commonly used properties and methods of these classes.

Sr.No.Topic & Description
1Reading from and Writing into Text filesIt involves reading from and writing into text files. The StreamReader and StreamWriter class helps to accomplish it.
2Reading from and Writing into Binary filesIt involves reading from and writing into binary files. The BinaryReader and BinaryWriter class helps to accomplish this.
3Manipulating the Windows file systemIt gives a C# programamer the ability to browse and locate Windows files and directories.

C# Exception Handling

An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.

Exceptions provide a way to transfer control from one part of a program to another. C# exception handling is built upon four keywords: trycatchfinally, and throw.

  • try − A try block identifies a block of code for which particular exceptions is activated. It is followed by one or more catch blocks.
  • catch − A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.
  • finally − The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.
  • throw − A program throws an exception when a problem shows up. This is done using a throw keyword.

Syntax

Assuming a block raises an exception, a method catches an exception using a combination of the try and catch keywords. A try/catch block is placed around the code that might generate an exception. Code within a try/catch block is referred to as protected code, and the syntax for using try/catch looks like the following −

try {
   // statements causing exception
} catch( ExceptionName e1 ) {
   // error handling code
} catch( ExceptionName e2 ) {
   // error handling code
} catch( ExceptionName eN ) {
   // error handling code
} finally {
   // statements to be executed
}

You can list down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situations.

Exception Classes in C#

C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.

The System.ApplicationException class supports exceptions generated by application programs. Hence the exceptions defined by the programmers should derive from this class.

The System.SystemException class is the base class for all predefined system exception.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class −

Sr.No.Exception Class & Description
1System.IO.IOExceptionHandles I/O errors.
2System.IndexOutOfRangeExceptionHandles errors generated when a method refers to an array index out of range.
3System.ArrayTypeMismatchExceptionHandles errors generated when type is mismatched with the array type.
4System.NullReferenceExceptionHandles errors generated from referencing a null object.
5System.DivideByZeroExceptionHandles errors generated from dividing a dividend with zero.
6System.InvalidCastExceptionHandles errors generated during typecasting.
7System.OutOfMemoryExceptionHandles errors generated from insufficient free memory.
8System.StackOverflowExceptionHandles errors generated from stack overflow.

Handling Exceptions

C# provides a structured solution to the exception handling in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handling statements.

These error handling blocks are implemented using the trycatch, and finally keywords. Following is an example of throwing an exception when dividing by zero condition occurs −Live Demo

using System;

namespace ErrorHandlingApplication {
   class DivNumbers {
      int result;
      
      DivNumbers() {
         result = 0;
      }
      public void division(int num1, int num2) {
         try {
            result = num1 / num2;
         } catch (DivideByZeroException e) {
            Console.WriteLine("Exception caught: {0}", e);
         } finally {
            Console.WriteLine("Result: {0}", result);
         }
      }
      static void Main(string[] args) {
         DivNumbers d = new DivNumbers();
         d.division(25, 0);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Exception caught: System.DivideByZeroException: Attempted to divide by zero. 
at ...
Result: 0

Creating User-Defined Exceptions

You can also define your own exception. User-defined exception classes are derived from the Exception class. The following example demonstrates this −Live Demo

using System;

namespace UserDefinedException {
   class TestTemperature {
      static void Main(string[] args) {
         Temperature temp = new Temperature();
         try {
            temp.showTemp();
         } catch(TempIsZeroException e) {
            Console.WriteLine("TempIsZeroException: {0}", e.Message);
         }
         Console.ReadKey();
      }
   }
}
public class TempIsZeroException: Exception {
   public TempIsZeroException(string message): base(message) {
   }
}
public class Temperature {
   int temperature = 0;
   
   public void showTemp() {
      
      if(temperature == 0) {
         throw (new TempIsZeroException("Zero Temperature found"));
      } else {
         Console.WriteLine("Temperature: {0}", temperature);
      }
   }
}

When the above code is compiled and executed, it produces the following result −

TempIsZeroException: Zero Temperature found

Throwing Objects

You can throw an object if it is either directly or indirectly derived from the System.Exception class. You can use a throw statement in the catch block to throw the present object as −

Catch(Exception e) {
   ...
   Throw e
}

C# Regular Expressions

regular expression is a pattern that could be matched against an input text. The .Net framework provides a regular expression engine that allows such matching. A pattern consists of one or more character literals, operators, or constructs.

Constructs for Defining Regular Expressions

There are various categories of characters, operators, and constructs that lets you to define regular expressions. Click the following links to find these constructs.

The Regex Class

The Regex class is used for representing a regular expression. It has the following commonly used methods −

Sr.No.Methods & Description
1public bool IsMatch(string input)Indicates whether the regular expression specified in the Regex constructor finds a match in a specified input string.
2public bool IsMatch(string input, int startat)Indicates whether the regular expression specified in the Regex constructor finds a match in the specified input string, beginning at the specified starting position in the string.
3public static bool IsMatch(string input, string pattern)Indicates whether the specified regular expression finds a match in the specified input string.
4public MatchCollection Matches(string input)Searches the specified input string for all occurrences of a regular expression.
5public string Replace(string input, string replacement)In a specified input string, replaces all strings that match a regular expression pattern with a specified replacement string.
6public string[] Split(string input)Splits an input string into an array of substrings at the positions defined by a regular expression pattern specified in the Regex constructor.

For the complete list of methods and properties, please read the Microsoft documentation on C#.

Example 1

The following example matches words that start with ‘S’ −Live Demo

using System;
using System.Text.RegularExpressions;

namespace RegExApplication {
   class Program {
      private static void showMatch(string text, string expr) {
         Console.WriteLine("The Expression: " + expr);
         MatchCollection mc = Regex.Matches(text, expr);
         
         foreach (Match m in mc) {
            Console.WriteLine(m);
         }
      }
      static void Main(string[] args) {
         string str = "A Thousand Splendid Suns";
         
         Console.WriteLine("Matching words that start with 'S': ");
         showMatch(str, @"\bS\S*");
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Matching words that start with 'S':
The Expression: \bS\S*
Splendid
Suns

Example 2

The following example matches words that start with ‘m’ and ends with ‘e’ −Live Demo

using System;
using System.Text.RegularExpressions;

namespace RegExApplication {
   class Program {
      private static void showMatch(string text, string expr) {
         Console.WriteLine("The Expression: " + expr);
         MatchCollection mc = Regex.Matches(text, expr);
         
         foreach (Match m in mc) {
            Console.WriteLine(m);
         }
      }
      static void Main(string[] args) {
         string str = "make maze and manage to measure it";

         Console.WriteLine("Matching words start with 'm' and ends with 'e':");
         showMatch(str, @"\bm\S*e\b");
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Matching words start with 'm' and ends with 'e':
The Expression: \bm\S*e\b
make
maze
manage
measure

Example 3

This example replaces extra white space −Live Demo

using System;
using System.Text.RegularExpressions;

namespace RegExApplication {
   class Program {
      static void Main(string[] args) {
         string input = "Hello   World   ";
         string pattern = "\\s+";
         string replacement = " ";
         
         Regex rgx = new Regex(pattern);
         string result = rgx.Replace(input, replacement);

         Console.WriteLine("Original String: {0}", input);
         Console.WriteLine("Replacement String: {0}", result);    
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Original String: Hello World   
Replacement String: Hello World   

C# Preprocessor Directives

The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.

All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).

C# compiler does not have a separate preprocessor; however, the directives are processed as if there was one. In C# the preprocessor directives are used to help in conditional compilation. Unlike C and C++ directives, they are not used to create macros. A preprocessor directive must be the only instruction on a line.

Preprocessor Directives in C#

The following table lists the preprocessor directives available in C# −

Sr.No.Preprocessor Directive & Description
1#defineIt defines a sequence of characters, called symbol.
2#undefIt allows you to undefine a symbol.
3#ifIt allows testing a symbol or symbols to see if they evaluate to true.
4#elseIt allows to create a compound conditional directive, along with #if.
5#elifIt allows creating a compound conditional directive.
6#endifSpecifies the end of a conditional directive.
7#lineIt lets you modify the compiler’s line number and (optionally) the file name output for errors and warnings.
8#errorIt allows generating an error from a specific location in your code.
9#warningIt allows generating a level one warning from a specific location in your code.
10#regionIt lets you specify a block of code that you can expand or collapse when using the outlining feature of the Visual Studio Code Editor.
11#endregionIt marks the end of a #region block.

The #define Preprocessor

The #define preprocessor directive creates symbolic constants.

#define lets you define a symbol such that, by using the symbol as the expression passed to the #if directive, the expression evaluates to true. Its syntax is as follows −

#define symbol

The following program illustrates this −Live Demo

#define PI 
using System;

namespace PreprocessorDAppl {
   class Program {
      static void Main(string[] args) {
         #if (PI)
            Console.WriteLine("PI is defined");
         #else
            Console.WriteLine("PI is not defined");
         #endif
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

PI is defined

Conditional Directives

You can use the #if directive to create a conditional directive. Conditional directives are useful for testing a symbol or symbols to check if they evaluate to true. If they do evaluate to true, the compiler evaluates all the code between the #if and the next directive.

Syntax for conditional directive is −

#if symbol [operator symbol]...

Where, symbol is the name of the symbol you want to test. You can also use true and false or prepend the symbol with the negation operator.

The operator symbol is the operator used for evaluating the symbol. Operators could be either of the following −

  • == (equality)
  • != (inequality)
  • && (and)
  • || (or)

You can also group symbols and operators with parentheses. Conditional directives are used for compiling code for a debug build or when compiling for a specific configuration. A conditional directive beginning with a #if directive must explicitly be terminated with a #endif directive.

The following program demonstrates use of conditional directives −Live Demo

#define DEBUG
#define VC_V10
using System;

public class TestClass {
   public static void Main() {
      #if (DEBUG && !VC_V10)
         Console.WriteLine("DEBUG is defined");
      #elif (!DEBUG && VC_V10)
         Console.WriteLine("VC_V10 is defined");
      #elif (DEBUG && VC_V10)
         Console.WriteLine("DEBUG and VC_V10 are defined");
      #else
         Console.WriteLine("DEBUG and VC_V10 are not defined");
      #endif
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

DEBUG and VC_V10 are defined

C# Namespaces

namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another.

Defining a Namespace

A namespace definition begins with the keyword namespace followed by the namespace name as follows −

namespace namespace_name {
   // code declarations
}

To call the namespace-enabled version of either function or variable, prepend the namespace name as follows −

namespace_name.item_name;

The following program demonstrates use of namespaces −Live Demo

using System;

namespace first_space {
   class namespace_cl {
      public void func() {
         Console.WriteLine("Inside first_space");
      }
   }
}
namespace second_space {
   class namespace_cl {
      public void func() {
         Console.WriteLine("Inside second_space");
      }
   }
}
class TestClass {
   static void Main(string[] args) {
      first_space.namespace_cl fc = new first_space.namespace_cl();
      second_space.namespace_cl sc = new second_space.namespace_cl();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

Inside first_space
Inside second_space

The using Keyword

The using keyword states that the program is using the names in the given namespace. For example, we are using the System namespace in our programs. The class Console is defined there. We just write −

Console.WriteLine ("Hello there");

We could have written the fully qualified name as −

System.Console.WriteLine("Hello there");

You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. The namespace is thus implied for the following code −

Let us rewrite our preceding example, with using directive −Live Demo

using System;
using first_space;
using second_space;

namespace first_space {
   class abc {
      public void func() {
         Console.WriteLine("Inside first_space");
      }
   }
}
namespace second_space {
   class efg {
      public void func() {
         Console.WriteLine("Inside second_space");
      }
   }
}   
class TestClass {
   static void Main(string[] args) {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

Inside first_space
Inside second_space

Nested Namespaces

You can define one namespace inside another namespace as follows −

namespace namespace_name1 {
   
   // code declarations
   namespace namespace_name2 {
      // code declarations
   }
}

You can access members of nested namespace by using the dot (.) operator as follows −Live Demo

using System;
using first_space;
using first_space.second_space;

namespace first_space {
   class abc {
      public void func() {
         Console.WriteLine("Inside first_space");
      }
   }
   namespace second_space {
      class efg {
         public void func() {
            Console.WriteLine("Inside second_space");
         }
      }
   }   
}
class TestClass {
   static void Main(string[] args) {
      abc fc = new abc();
      efg sc = new efg();
      fc.func();
      sc.func();
      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

Inside first_space
Inside second_space

C# Operator Overloading

You can redefine or overload most of the built-in operators available in C#. Thus a programmer can use operators with user-defined types as well. Overloaded operators are functions with special names the keyword operator followed by the symbol for the operator being defined. similar to any other function, an overloaded operator has a return type and a parameter list.

For example, go through the following function −

public static Box operator+ (Box b, Box c) {
   Box box = new Box();
   box.length = b.length + c.length;
   box.breadth = b.breadth + c.breadth;
   box.height = b.height + c.height;
   return box;
}

The above function implements the addition operator (+) for a user-defined class Box. It adds the attributes of two Box objects and returns the resultant Box object.

Implementing the Operator Overloading

The following program shows the complete implementation −Live Demo

using System;

namespace OperatorOvlApplication {
   class Box {
      private double length;   // Length of a box
      private double breadth;  // Breadth of a box
      private double height;   // Height of a box

      public double getVolume() {
         return length * breadth * height;
      }
      public void setLength( double len ) {
         length = len;
      }
      public void setBreadth( double bre ) {
         breadth = bre;
      }
      public void setHeight( double hei ) {
         height = hei;
      }
      
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c) {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }
   }
   class Tester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();   // Declare Box2 of type Box
         Box Box3 = new Box();   // Declare Box3 of type Box
         double volume = 0.0;    // Store the volume of a box here

         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);

         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);

         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);

         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);

         // Add two object as follows:
         Box3 = Box1 + Box2;

         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Volume of Box1 : 210
Volume of Box2 : 1560
Volume of Box3 : 5400

Overloadable and Non-Overloadable Operators

The following table describes the overload ability of the operators in C# −

Sr.No.Operators & Description
1+, -, !, ~, ++, —These unary operators take one operand and can be overloaded.
2+, -, *, /, %These binary operators take one operand and can be overloaded.
3==, !=, <, >, <=, >=The comparison operators can be overloaded.
4&&, ||The conditional logical operators cannot be overloaded directly.
5+=, -=, *=, /=, %=The assignment operators cannot be overloaded.
6=, ., ?:, ->, new, is, sizeof, typeofThese operators cannot be overloaded.

Example

In the light of the above discussions, let us extend the preceding example, and overload few more operators −Live Demo

using System;

namespace OperatorOvlApplication {
   class Box {
      private double length;    // Length of a box
      private double breadth;   // Breadth of a box
      private double height;    // Height of a box
      
      public double getVolume() {
         return length * breadth * height;
      }
      public void setLength( double len ) {
         length = len;
      }
      public void setBreadth( double bre ) {
         breadth = bre;
      }
      public void setHeight( double hei ) {
         height = hei;
      }
      
      // Overload + operator to add two Box objects.
      public static Box operator+ (Box b, Box c) {
         Box box = new Box();
         box.length = b.length + c.length;
         box.breadth = b.breadth + c.breadth;
         box.height = b.height + c.height;
         return box;
      }
      public static bool operator == (Box lhs, Box rhs) {
         bool status = false;
         if (lhs.length == rhs.length && lhs.height == rhs.height 
            && lhs.breadth == rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public static bool operator !=(Box lhs, Box rhs) {
         bool status = false;
         
         if (lhs.length != rhs.length || lhs.height != rhs.height || 
            lhs.breadth != rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public static bool operator <(Box lhs, Box rhs) {
         bool status = false;
         
         if (lhs.length < rhs.length && lhs.height < rhs.height 
            && lhs.breadth < rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public static bool operator >(Box lhs, Box rhs) {
         bool status = false;
         
         if (lhs.length > rhs.length && lhs.height > 
            rhs.height && lhs.breadth > rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public static bool operator <=(Box lhs, Box rhs) {
         bool status = false;
         
         if (lhs.length <= rhs.length && lhs.height 
            <= rhs.height && lhs.breadth <= rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public static bool operator >=(Box lhs, Box rhs) {
         bool status = false;
         
         if (lhs.length >= rhs.length && lhs.height 
            >= rhs.height && lhs.breadth >= rhs.breadth) {
            
            status = true;
         }
         return status;
      }
      public override string ToString() {
         return String.Format("({0}, {1}, {2})", length, breadth, height);
      }
   }
   class Tester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();   // Declare Box2 of type Box
         Box Box3 = new Box();   // Declare Box3 of type Box
         Box Box4 = new Box();
         double volume = 0.0;    // Store the volume of a box here
         
         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);
         
         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);
         
         //displaying the Boxes using the overloaded ToString():
         Console.WriteLine("Box 1: {0}", Box1.ToString());
         Console.WriteLine("Box 2: {0}", Box2.ToString());
         
         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}", volume);
         
         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);
         
         // Add two object as follows:
         Box3 = Box1 + Box2;
         Console.WriteLine("Box 3: {0}", Box3.ToString());
         
         // volume of box 3
         volume = Box3.getVolume();
         Console.WriteLine("Volume of Box3 : {0}", volume);
         
         //comparing the boxes
         if (Box1 > Box2)
            Console.WriteLine("Box1 is greater than Box2");
         else
            Console.WriteLine("Box1 is not greater than Box2");
         
         if (Box1 < Box2)
            Console.WriteLine("Box1 is less than Box2");
         else
            Console.WriteLine("Box1 is not less than Box2");
         
         if (Box1 >= Box2)
            Console.WriteLine("Box1 is greater or equal to Box2");
         else
            Console.WriteLine("Box1 is not greater or equal to Box2");
         
         if (Box1 <= Box2)
            Console.WriteLine("Box1 is less or equal to Box2");
         else
            Console.WriteLine("Box1 is not less or equal to Box2");
         
         if (Box1 != Box2)
            Console.WriteLine("Box1 is not equal to Box2");
         else
            Console.WriteLine("Box1 is not greater or equal to Box2");
         Box4 = Box3;
         
         if (Box3 == Box4)
            Console.WriteLine("Box3 is equal to Box4");
         else
            Console.WriteLine("Box3 is not equal to Box4");

         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Box 1: (6, 7, 5)
Box 2: (12, 13, 10)
Volume of Box1 : 210
Volume of Box2 : 1560
Box 3: (18, 20, 15)
Volume of Box3 : 5400
Box1 is not greater than Box2
Box1 is less than Box2
Box1 is not greater or equal to Box2
Box1 is less or equal to Box2
Box1 is not equal to Box2
Box3 is equal to Box4

C# Polymorphism

The word polymorphism means having many forms. In object-oriented programming paradigm, polymorphism is often expressed as ‘one interface, multiple functions’.

Polymorphism can be static or dynamic. In static polymorphism, the response to a function is determined at the compile time. In dynamic polymorphism, it is decided at run-time.

Static Polymorphism

The mechanism of linking a function with an object during compile time is called early binding. It is also called static binding. C# provides two techniques to implement static polymorphism. They are −

  • Function overloading
  • Operator overloading

We discuss operator overloading in next chapter.

Function Overloading

You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You cannot overload function declarations that differ only by return type.

The following example shows using function print() to print different data types −Live Demo

using System;

namespace PolymorphismApplication {
   class Printdata {
      void print(int i) {
         Console.WriteLine("Printing int: {0}", i );
      }
      void print(double f) {
         Console.WriteLine("Printing float: {0}" , f);
      }
      void print(string s) {
         Console.WriteLine("Printing string: {0}", s);
      }
      static void Main(string[] args) {
         Printdata p = new Printdata();
         
         // Call print to print integer
         p.print(5);
         
         // Call print to print float
         p.print(500.263);
         
         // Call print to print string
         p.print("Hello C++");
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Printing int: 5
Printing float: 500.263
Printing string: Hello C++

Dynamic Polymorphism

C# allows you to create abstract classes that are used to provide partial class implementation of an interface. Implementation is completed when a derived class inherits from it. Abstract classes contain abstract methods, which are implemented by the derived class. The derived classes have more specialized functionality.

Here are the rules about abstract classes −

  • You cannot create an instance of an abstract class
  • You cannot declare an abstract method outside an abstract class
  • When a class is declared sealed, it cannot be inherited, abstract classes cannot be declared sealed.

The following program demonstrates an abstract class −Live Demo

using System;

namespace PolymorphismApplication {
   abstract class Shape {
      public abstract int area();
   }
   
   class Rectangle:  Shape {
      private int length;
      private int width;
      
      public Rectangle( int a = 0, int b = 0) {
         length = a;
         width = b;
      }
      public override int area () { 
         Console.WriteLine("Rectangle class area :");
         return (width * length); 
      }
   }
   class RectangleTester {
      static void Main(string[] args) {
         Rectangle r = new Rectangle(10, 7);
         double a = r.area();
         Console.WriteLine("Area: {0}",a);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Rectangle class area :
Area: 70

When you have a function defined in a class that you want to be implemented in an inherited class(es), you use virtual functions. The virtual functions could be implemented differently in different inherited class and the call to these functions will be decided at runtime.

Dynamic polymorphism is implemented by abstract classes and virtual functions.

The following program demonstrates this −Live Demo

using System;

namespace PolymorphismApplication {
   class Shape {
      protected int width, height;
      
      public Shape( int a = 0, int b = 0) {
         width = a;
         height = b;
      }
      public virtual int area() {
         Console.WriteLine("Parent class area :");
         return 0;
      }
   }
   class Rectangle: Shape {
      public Rectangle( int a = 0, int b = 0): base(a, b) {

      }
      public override int area () {
         Console.WriteLine("Rectangle class area :");
         return (width * height); 
      }
   }
   class Triangle: Shape {
      public Triangle(int a = 0, int b = 0): base(a, b) {
      }
      public override int area() {
         Console.WriteLine("Triangle class area :");
         return (width * height / 2); 
      }
   }
   class Caller {
      public void CallArea(Shape sh) {
         int a;
         a = sh.area();
         Console.WriteLine("Area: {0}", a);
      }
   }  
   class Tester {
      static void Main(string[] args) {
         Caller c = new Caller();
         Rectangle r = new Rectangle(10, 7);
         Triangle t = new Triangle(10, 5);
         
         c.CallArea(r);
         c.CallArea(t);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Rectangle class area:
Area: 70
Triangle class area:
Area: 25

C# Classes

When you define a class, you define a blueprint for a data type. This does not actually define any data, but it does define what the class name means. That is, what an object of the class consists of and what operations can be performed on that object. Objects are instances of a class. The methods and variables that constitute a class are called members of the class.

Defining a Class

A class definition starts with the keyword class followed by the class name; and the class body enclosed by a pair of curly braces. Following is the general form of a class definition −

<access specifier> class  class_name {
   // member variables
   <access specifier> <data type> variable1;
   <access specifier> <data type> variable2;
   ...
   <access specifier> <data type> variableN;
   // member methods
   <access specifier> <return type> method1(parameter_list) {
      // method body
   }
   <access specifier> <return type> method2(parameter_list) {
      // method body
   }
   ...
   <access specifier> <return type> methodN(parameter_list) {
      // method body
   }
}

Note −

  • Access specifiers specify the access rules for the members as well as the class itself. If not mentioned, then the default access specifier for a class type is internal. Default access for the members is private.
  • Data type specifies the type of variable, and return type specifies the data type of the data the method returns, if any.
  • To access the class members, you use the dot (.) operator.
  • The dot operator links the name of an object with the name of a member.

The following example illustrates the concepts discussed so far −Live Demo

using System;

namespace BoxApplication {
   class Box {
      public double length;   // Length of a box
      public double breadth;  // Breadth of a box
      public double height;   // Height of a box
   }
   class Boxtester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();   // Declare Box2 of type Box
         double volume = 0.0;    // Store the volume of a box here

         // box 1 specification
         Box1.height = 5.0;
         Box1.length = 6.0;
         Box1.breadth = 7.0;

         // box 2 specification
         Box2.height = 10.0;
         Box2.length = 12.0;
         Box2.breadth = 13.0;
           
         // volume of box 1
         volume = Box1.height * Box1.length * Box1.breadth;
         Console.WriteLine("Volume of Box1 : {0}",  volume);

         // volume of box 2
         volume = Box2.height * Box2.length * Box2.breadth;
         Console.WriteLine("Volume of Box2 : {0}", volume);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Volume of Box1 : 210
Volume of Box2 : 1560

Member Functions and Encapsulation

A member function of a class is a function that has its definition or its prototype within the class definition similar to any other variable. It operates on any object of the class of which it is a member, and has access to all the members of a class for that object.

Member variables are the attributes of an object (from design perspective) and they are kept private to implement encapsulation. These variables can only be accessed using the public member functions.

Let us put above concepts to set and get the value of different class members in a class −Live Demo

using System;

namespace BoxApplication {
   class Box {
      private double length;   // Length of a box
      private double breadth;  // Breadth of a box
      private double height;   // Height of a box
      
      public void setLength( double len ) {
         length = len;
      }
      public void setBreadth( double bre ) {
         breadth = bre;
      }
      public void setHeight( double hei ) {
         height = hei;
      }
      public double getVolume() {
         return length * breadth * height;
      }
   }
   class Boxtester {
      static void Main(string[] args) {
         Box Box1 = new Box();   // Declare Box1 of type Box
         Box Box2 = new Box();
         double volume;
         
         // Declare Box2 of type Box
         // box 1 specification
         Box1.setLength(6.0);
         Box1.setBreadth(7.0);
         Box1.setHeight(5.0);
         
         // box 2 specification
         Box2.setLength(12.0);
         Box2.setBreadth(13.0);
         Box2.setHeight(10.0);
         
         // volume of box 1
         volume = Box1.getVolume();
         Console.WriteLine("Volume of Box1 : {0}" ,volume);
         
         // volume of box 2
         volume = Box2.getVolume();
         Console.WriteLine("Volume of Box2 : {0}", volume);
         
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Volume of Box1 : 210
Volume of Box2 : 1560

C# Constructors

A class constructor is a special member function of a class that is executed whenever we create new objects of that class.

A constructor has exactly the same name as that of class and it does not have any return type. Following example explains the concept of constructor −Live Demo

using System;

namespace LineApplication {
   class Line {
      private double length;   // Length of a line
      
      public Line() {
         Console.WriteLine("Object is being created");
      }
      public void setLength( double len ) {
         length = len;
      }
      public double getLength() {
         return length;
      }

      static void Main(string[] args) {
         Line line = new Line();    
         
         // set line length
         line.setLength(6.0);
         Console.WriteLine("Length of line : {0}", line.getLength());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Object is being created
Length of line : 6

default constructor does not have any parameter but if you need, a constructor can have parameters. Such constructors are called parameterized constructors. This technique helps you to assign initial value to an object at the time of its creation as shown in the following example −Live Demo

using System;

namespace LineApplication {
   class Line {
      private double length;   // Length of a line
      
      public Line(double len) {  //Parameterized constructor
         Console.WriteLine("Object is being created, length = {0}", len);
         length = len;
      }
      public void setLength( double len ) {
         length = len;
      }
      public double getLength() {
         return length;
      }
      static void Main(string[] args) {
         Line line = new Line(10.0);
         Console.WriteLine("Length of line : {0}", line.getLength()); 
         
         // set line length
         line.setLength(6.0);
         Console.WriteLine("Length of line : {0}", line.getLength()); 
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Object is being created, length = 10
Length of line : 10
Length of line : 6

C# Destructors

destructor is a special member function of a class that is executed whenever an object of its class goes out of scope. A destructor has exactly the same name as that of the class with a prefixed tilde (~) and it can neither return a value nor can it take any parameters.

Destructor can be very useful for releasing memory resources before exiting the program. Destructors cannot be inherited or overloaded.

Following example explains the concept of destructor −Live Demo

using System;

namespace LineApplication {
   class Line {
      private double length;   // Length of a line
      
      public Line() {   // constructor
         Console.WriteLine("Object is being created");
      }
      ~Line() {   //destructor
         Console.WriteLine("Object is being deleted");
      }
      public void setLength( double len ) {
         length = len;
      }
      public double getLength() {
         return length;
      }
      static void Main(string[] args) {
         Line line = new Line();

         // set line length
         line.setLength(6.0);
         Console.WriteLine("Length of line : {0}", line.getLength());           
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Object is being created
Length of line : 6
Object is being deleted

Static Members of a C# Class

We can define class members as static using the static keyword. When we declare a member of a class as static, it means no matter how many objects of the class are created, there is only one copy of the static member.

The keyword static implies that only one instance of the member exists for a class. Static variables are used for defining constants because their values can be retrieved by invoking the class without creating an instance of it. Static variables can be initialized outside the member function or class definition. You can also initialize static variables inside the class definition.

The following example demonstrates the use of static variables −Live Demo

using System;

namespace StaticVarApplication {
   class StaticVar {
      public static int num;
      
      public void count() {
         num++;
      }
      public int getNum() {
         return num;
      }
   }
   class StaticTester {
      static void Main(string[] args) {
         StaticVar s1 = new StaticVar();
         StaticVar s2 = new StaticVar();
         
         s1.count();
         s1.count();
         s1.count();
         
         s2.count();
         s2.count();
         s2.count();
         
         Console.WriteLine("Variable num for s1: {0}", s1.getNum());
         Console.WriteLine("Variable num for s2: {0}", s2.getNum());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Variable num for s1: 6
Variable num for s2: 6

You can also declare a member function as static. Such functions can access only static variables. The static functions exist even before the object is created. The following example demonstrates the use of static functions −Live Demo

using System;

namespace StaticVarApplication {
   class StaticVar {
      public static int num;
      
      public void count() {
         num++;
      }
      public static int getNum() {
         return num;
      }
   }
   class StaticTester {
      static void Main(string[] args) {
         StaticVar s = new StaticVar();
         
         s.count();
         s.count();
         s.count();
         
         Console.WriteLine("Variable num: {0}", StaticVar.getNum());
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Variable num: 3

C# Enums

An enumeration is a set of named integer constants. An enumerated type is declared using the enum keyword.

C# enumerations are value data type. In other words, enumeration contains its own values and cannot inherit or cannot pass inheritance.

Declaring enum Variable

The general syntax for declaring an enumeration is −

enum <enum_name> {
   enumeration list 
};

Where,

  • The enum_name specifies the enumeration type name.
  • The enumeration list is a comma-separated list of identifiers.

Each of the symbols in the enumeration list stands for an integer value, one greater than the symbol that precedes it. By default, the value of the first enumeration symbol is 0. For example −

enum Days { Sun, Mon, tue, Wed, thu, Fri, Sat };

Example

The following example demonstrates use of enum variable −Live Demo

using System;

namespace EnumApplication {
   class EnumProgram {
      enum Days { Sun, Mon, tue, Wed, thu, Fri, Sat };

      static void Main(string[] args) {
         int WeekdayStart = (int)Days.Mon;
         int WeekdayEnd = (int)Days.Fri;
         
         Console.WriteLine("Monday: {0}", WeekdayStart);
         Console.WriteLine("Friday: {0}", WeekdayEnd);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Monday: 1
Friday: 5

C# Structures

In C#, a structure is a value type data type. It helps you to make a single variable hold related data of various data types. The struct keyword is used for creating a structure.

Structures are used to represent a record. Suppose you want to keep track of your books in a library. You might want to track the following attributes about each book −

  • Title
  • Author
  • Subject
  • Book ID

Defining a Structure

To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member for your program.

For example, here is the way you can declare the Book structure −

struct Books {
   public string title;
   public string author;
   public string subject;
   public int book_id;
};  

The following program shows the use of the structure −Live Demo

using System;

struct Books {
   public string title;
   public string author;
   public string subject;
   public int book_id;
};  

public class testStructure {
   public static void Main(string[] args) {
      Books Book1;   /* Declare Book1 of type Book */
      Books Book2;   /* Declare Book2 of type Book */

      /* book 1 specification */
      Book1.title = "C Programming";
      Book1.author = "Nuha Ali"; 
      Book1.subject = "C Programming Tutorial";
      Book1.book_id = 6495407;

      /* book 2 specification */
      Book2.title = "Telecom Billing";
      Book2.author = "Zara Ali";
      Book2.subject =  "Telecom Billing Tutorial";
      Book2.book_id = 6495700;

      /* print Book1 info */
      Console.WriteLine( "Book 1 title : {0}", Book1.title);
      Console.WriteLine("Book 1 author : {0}", Book1.author);
      Console.WriteLine("Book 1 subject : {0}", Book1.subject);
      Console.WriteLine("Book 1 book_id :{0}", Book1.book_id);

      /* print Book2 info */
      Console.WriteLine("Book 2 title : {0}", Book2.title);
      Console.WriteLine("Book 2 author : {0}", Book2.author);
      Console.WriteLine("Book 2 subject : {0}", Book2.subject);
      Console.WriteLine("Book 2 book_id : {0}", Book2.book_id);       

      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700

Features of C# Structures

You have already used a simple structure named Books. Structures in C# are quite different from that in traditional C or C++. The C# structures have the following features −

  • Structures can have methods, fields, indexers, properties, operator methods, and events.
  • Structures can have defined constructors, but not destructors. However, you cannot define a default constructor for a structure. The default constructor is automatically defined and cannot be changed.
  • Unlike classes, structures cannot inherit other structures or classes.
  • Structures cannot be used as a base for other structures or classes.
  • A structure can implement one or more interfaces.
  • Structure members cannot be specified as abstract, virtual, or protected.
  • When you create a struct object using the New operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the New operator.
  • If the New operator is not used, the fields remain unassigned and the object cannot be used until all the fields are initialized.

Class versus Structure

Classes and Structures have the following basic differences −

  • classes are reference types and structs are value types
  • structures do not support inheritance
  • structures cannot have default constructor

In the light of the above discussions, let us rewrite the previous example −Live Demo

using System;

struct Books {
   private string title;
   private string author;
   private string subject;
   private int book_id;
   
   public void getValues(string t, string a, string s, int id) {
      title = t;
      author = a;
      subject = s;
      book_id = id;
   }
   
   public void display() {
      Console.WriteLine("Title : {0}", title);
      Console.WriteLine("Author : {0}", author);
      Console.WriteLine("Subject : {0}", subject);
      Console.WriteLine("Book_id :{0}", book_id);
   }
};  

public class testStructure {

   public static void Main(string[] args) {
      Books Book1 = new Books();   /* Declare Book1 of type Book */
      Books Book2 = new Books();   /* Declare Book2 of type Book */

      /* book 1 specification */
      Book1.getValues("C Programming",
      "Nuha Ali", "C Programming Tutorial",6495407);

      /* book 2 specification */
      Book2.getValues("Telecom Billing",
      "Zara Ali", "Telecom Billing Tutorial", 6495700);

      /* print Book1 info */
      Book1.display();

      /* print Book2 info */
      Book2.display(); 

      Console.ReadKey();
   }
}

When the above code is compiled and executed, it produces the following result −

Title : C Programming
Author : Nuha Ali
Subject : C Programming Tutorial
Book_id : 6495407
Title : Telecom Billing
Author : Zara Ali
Subject : Telecom Billing Tutorial
Book_id : 6495700

C# Strings

In C#, you can use strings as array of characters, However, more common practice is to use the string keyword to declare a string variable. The string keyword is an alias for the System.String class.

Creating a String Object

You can create string object using one of the following methods −

  • By assigning a string literal to a String variable
  • By using a String class constructor
  • By using the string concatenation operator (+)
  • By retrieving a property or calling a method that returns a string
  • By calling a formatting method to convert a value or an object to its string representation

The following example demonstrates this −

using System;

namespace StringApplication {

   class Program {
   
      static void Main(string[] args) {
         //from string literal and string concatenation
         string fname, lname;
         fname = "Rowan";
         lname = "Atkinson";
			
         char []letters= { 'H', 'e', 'l', 'l','o' };
         string [] sarray={ "Hello", "From", "Tutorials", "Point" };
         
         string fullname = fname + lname;
         Console.WriteLine("Full Name: {0}", fullname);
         
         //by using string constructor { 'H', 'e', 'l', 'l','o' };
         string greetings = new string(letters);
         Console.WriteLine("Greetings: {0}", greetings);
         
         //methods returning string { "Hello", "From", "Tutorials", "Point" };
         string message = String.Join(" ", sarray);
         Console.WriteLine("Message: {0}", message);
         
         //formatting method to convert a value
         DateTime waiting = new DateTime(2012, 10, 10, 17, 58, 1);
         string chat = String.Format("Message sent at {0:t} on {0:D}", waiting);
         Console.WriteLine("Message: {0}", chat);
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Full Name: RowanAtkinson
Greetings: Hello
Message: Hello From Tutorials Point
Message: Message sent at 5:58 PM on Wednesday, October 10, 2012

Properties of the String Class

The String class has the following two properties −

Sr.No.Property & Description
1CharsGets the Char object at a specified position in the current String object.
2LengthGets the number of characters in the current String object.

Methods of the String Class

The String class has numerous methods that help you in working with the string objects. The following table provides some of the most commonly used methods −Given below is the list of methods of the String class.

You can visit MSDN library for the complete list of methods and String class constructors.

Examples

The following example demonstrates some of the methods mentioned above −

Comparing Strings

using System;

namespace StringApplication {

   class StringProg {
   
      static void Main(string[] args) {
         string str1 = "This is test";
         string str2 = "This is text";

         if (String.Compare(str1, str2) == 0) {
            Console.WriteLine(str1 + " and " + str2 +  " are equal.");
         } else {
            Console.WriteLine(str1 + " and " + str2 + " are not equal.");
         }
         Console.ReadKey() ;
      }
   }
}

When the above code is compiled and executed, it produces the following result −

This is test and This is text are not equal.

String Contains String

using System;

namespace StringApplication {

   class StringProg {
   
      static void Main(string[] args) {
         string str = "This is test";
         
         if (str.Contains("test")) {
            Console.WriteLine("The sequence 'test' was found.");
         }
         Console.ReadKey() ;
      }
   }
}

When the above code is compiled and executed, it produces the following result −

The sequence 'test' was found.

Getting a Substring

using System;

namespace StringApplication {

   class StringProg {
   
      static void Main(string[] args) {
         string str = "Last night I dreamt of San Pedro";
         Console.WriteLine(str);
         string substr = str.Substring(23);
         Console.WriteLine(substr);
      }
   }
}

When the above code is compiled and executed, it produces the following result −

San Pedro

Joining Strings

using System;

namespace StringApplication {

   class StringProg {
   
      static void Main(string[] args) {
         string[] starray = new string[]{"Down the way nights are dark",
            "And the sun shines daily on the mountain top",
            "I took a trip on a sailing ship",
            "And when I reached Jamaica",
            "I made a stop"};

         string str = String.Join("\n", starray);
         Console.WriteLine(str);
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Down the way nights are dark
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop

C# Arrays

An array stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type stored at contiguous memory locations.

Instead of declaring individual variables, such as number0, number1, …, and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and …, numbers[99] to represent individual variables. A specific element in an array is accessed by an index.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Arrays in C#

Declaring Arrays

To declare an array in C#, you can use the following syntax −

datatype[] arrayName;

where,

  • datatype is used to specify the type of elements in the array.
  • [ ] specifies the rank of the array. The rank specifies the size of the array.
  • arrayName specifies the name of the array.

For example,

double[] balance;

Initializing an Array

Declaring an array does not initialize the array in the memory. When the array variable is initialized, you can assign values to the array.

Array is a reference type, so you need to use the new keyword to create an instance of the array. For example,

double[] balance = new double[10];

Assigning Values to an Array

You can assign values to individual array elements, by using the index number, like −

double[] balance = new double[10];
balance[0] = 4500.0;

You can assign values to the array at the time of declaration, as shown −

double[] balance = { 2340.0, 4523.69, 3421.0};

You can also create and initialize an array, as shown −

int [] marks = new int[5]  { 99,  98, 92, 97, 95};

You may also omit the size of the array, as shown −

int [] marks = new int[]  { 99,  98, 92, 97, 95};

You can copy an array variable into another target array variable. In such case, both the target and source point to the same memory location −

int [] marks = new int[]  { 99,  98, 92, 97, 95};
int[] score = marks;

When you create an array, C# compiler implicitly initializes each array element to a default value depending on the array type. For example, for an int array all elements are initialized to 0.

Accessing Array Elements

An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example,

double salary = balance[9];

The following example, demonstrates the above-mentioned concepts declaration, assignment, and accessing arrays −Live Demo

using System;

namespace ArrayApplication {
   class MyArray {
      static void Main(string[] args) {
         int []  n = new int[10]; /* n is an array of 10 integers */
         int i,j;

         /* initialize elements of array n */
         for ( i = 0; i < 10; i++ ) {
            n[ i ] = i + 100;
         }
         
         /* output each array element's value */
         for (j = 0; j < 10; j++ ) {
            Console.WriteLine("Element[{0}] = {1}", j, n[j]);
         }
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109

Using the foreach Loop

In the previous example, we used a for loop for accessing each array element. You can also use a foreach statement to iterate through an array.Live Demo

using System;

namespace ArrayApplication {
   class MyArray {
      static void Main(string[] args) {
         int []  n = new int[10]; /* n is an array of 10 integers */
         
         /* initialize elements of array n */
         for ( int i = 0; i < 10; i++ ) {
            n[i] = i + 100;
         }
         
         /* output each array element's value */
         foreach (int j in n ) {
            int i = j-100;
            Console.WriteLine("Element[{0}] = {1}", i, j);
         }
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109

C# Arrays

There are following few important concepts related to array which should be clear to a C# programmer −

Sr.No.Concept & Description
1Multi-dimensional arraysC# supports multidimensional arrays. The simplest form of the multidimensional array is the two-dimensional array.
2Jagged arraysC# supports multidimensional arrays, which are arrays of arrays.
3Passing arrays to functionsYou can pass to the function a pointer to an array by specifying the array’s name without an index.
4Param arraysThis is used for passing unknown number of parameters to a function.
5The Array ClassDefined in System namespace, it is the base class to all arrays, and provides various properties and methods for working with arrays.

C# Nullables

C# provides a special data types, the nullable types, to which you can assign normal range of values as well as null values.

For example, you can store any value from -2,147,483,648 to 2,147,483,647 or null in a Nullable<Int32> variable. Similarly, you can assign true, false, or null in a Nullable<bool> variable. Syntax for declaring a nullable type is as follows −

< data_type> ? <variable_name> = null;

The following example demonstrates use of nullable data types −Live Demo

using System;

namespace CalculatorApplication {
   class NullablesAtShow {
      static void Main(string[] args) {
         int? num1 = null;
         int? num2 = 45;
         
         double? num3 = new double?();
         double? num4 = 3.14157;
         
         bool? boolval = new bool?();

         // display the values
         Console.WriteLine("Nullables at Show: {0}, {1}, {2}, {3}", num1, num2, num3, num4);
         Console.WriteLine("A Nullable boolean value: {0}", boolval);
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Nullables at Show: , 45,  , 3.14157
A Nullable boolean value:

The Null Coalescing Operator (??)

The null coalescing operator is used with the nullable value types and reference types. It is used for converting an operand to the type of another nullable (or not) value type operand, where an implicit conversion is possible.

If the value of the first operand is null, then the operator returns the value of the second operand, otherwise it returns the value of the first operand. The following example explains this −Live Demo

using System;

namespace CalculatorApplication {
   class NullablesAtShow {
      static void Main(string[] args) {
         double? num1 = null;
         double? num2 = 3.14157;
         double num3;
         
         num3 = num1 ?? 5.34;      
         Console.WriteLine(" Value of num3: {0}", num3);
         
         num3 = num2 ?? 5.34;
         Console.WriteLine(" Value of num3: {0}", num3);
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of num3: 5.34
Value of num3: 3.14157

C# Methods

A method is a group of statements that together perform a task. Every C# program has at least one class with a method named Main.

To use a method, you need to −

  • Define the method
  • Call the method

Defining Methods in C#

When you define a method, you basically declare the elements of its structure. The syntax for defining a method in C# is as follows −

<Access Specifier> <Return Type> <Method Name>(Parameter List) {
   Method Body
}

Following are the various elements of a method −

  • Access Specifier − This determines the visibility of a variable or a method from another class.
  • Return type − A method may return a value. The return type is the data type of the value the method returns. If the method is not returning any values, then the return type is void.
  • Method name − Method name is a unique identifier and it is case sensitive. It cannot be same as any other identifier declared in the class.
  • Parameter list − Enclosed between parentheses, the parameters are used to pass and receive data from a method. The parameter list refers to the type, order, and number of the parameters of a method. Parameters are optional; that is, a method may contain no parameters.
  • Method body − This contains the set of instructions needed to complete the required activity.

Example

Following code snippet shows a function FindMax that takes two integer values and returns the larger of the two. It has public access specifier, so it can be accessed from outside the class using an instance of the class.

class NumberManipulator {

   public int FindMax(int num1, int num2) {
      /* local variable declaration */
      int result;

      if (num1 > num2)
         result = num1;
      else
         result = num2;

      return result;
   }
   ...
}

Calling Methods in C#

You can call a method using the name of the method. The following example illustrates this −Live Demo

using System;

namespace CalculatorApplication {
   class NumberManipulator {
      public int FindMax(int num1, int num2) {
         /* local variable declaration */
         int result;
         
         if (num1 > num2)
            result = num1;
         else
            result = num2;
         return result;
      }
      
      static void Main(string[] args) {
         /* local variable definition */
         int a = 100;
         int b = 200;
         int ret;
         NumberManipulator n = new NumberManipulator();

         //calling the FindMax method
         ret = n.FindMax(a, b);
         Console.WriteLine("Max value is : {0}", ret );
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Max value is : 200

You can also call public method from other classes by using the instance of the class. For example, the method FindMax belongs to the NumberManipulator class, you can call it from another class Test.Live Demo

using System;

namespace CalculatorApplication {
   class NumberManipulator {
      public int FindMax(int num1, int num2) {
         /* local variable declaration */
         int result;
         
         if(num1 > num2)
            result = num1;
         else
            result = num2;
         
         return result;
      }
   }
   class Test {
      static void Main(string[] args) {
         /* local variable definition */
         int a = 100;
         int b = 200;
         int ret;
         NumberManipulator n = new NumberManipulator();
         
         //calling the FindMax method
         ret = n.FindMax(a, b);
         Console.WriteLine("Max value is : {0}", ret );
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Max value is : 200

Recursive Method Call

A method can call itself. This is known as recursion. Following is an example that calculates factorial for a given number using a recursive function −Live Demo

using System;

namespace CalculatorApplication {
   class NumberManipulator {
      public int factorial(int num) {
         /* local variable declaration */
         int result;
         if (num == 1) {
            return 1;
         } else {
            result = factorial(num - 1) * num;
            return result;
         }
      }
      static void Main(string[] args) {
         NumberManipulator n = new NumberManipulator();
         //calling the factorial method {0}", n.factorial(6));
         Console.WriteLine("Factorial of 7 is : {0}", n.factorial(7));
         Console.WriteLine("Factorial of 8 is : {0}", n.factorial(8));
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Factorial of 6 is: 720
Factorial of 7 is: 5040
Factorial of 8 is: 40320

Passing Parameters to a Method

When method with parameters is called, you need to pass the parameters to the method. There are three ways that parameters can be passed to a method −

Sr.No.Mechanism & Description
1Value parametersThis method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument.
2Reference parametersThis method copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.
3Output parametersThis method helps in returning more than one value.

C# Encapsulation

Encapsulation is defined ‘as the process of enclosing one or more items within a physical or logical package’. Encapsulation, in object oriented programming methodology, prevents access to implementation details.

Abstraction and encapsulation are related features in object oriented programming. Abstraction allows making relevant information visible and encapsulation enables a programmer to implement the desired level of abstraction.

Encapsulation is implemented by using access specifiers. An access specifier defines the scope and visibility of a class member. C# supports the following access specifiers −

  • Public
  • Private
  • Protected
  • Internal
  • Protected internal

Public Access Specifier

Public access specifier allows a class to expose its member variables and member functions to other functions and objects. Any public member can be accessed from outside the class.

The following example illustrates this −Live Demo

using System;

namespace RectangleApplication {
   class Rectangle {
      //member variables
      public double length;
      public double width;
      
      public double GetArea() {
         return length * width;
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.length = 4.5;
         r.width = 3.5;
         r.Display();
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 3.5
Area: 15.75

In the preceding example, the member variables length and width are declared public, so they can be accessed from the function Main() using an instance of the Rectangle class, named r.

The member function Display() and GetArea() can also access these variables directly without using any instance of the class.

The member functions Display() is also declared public, so it can also be accessed from Main() using an instance of the Rectangle class, named r.

Private Access Specifier

Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.

The following example illustrates this −Live Demo

using System;

namespace RectangleApplication {
   class Rectangle {
      //member variables
      private double length;
      private double width;
      
      public void Acceptdetails() {
         Console.WriteLine("Enter Length: ");
         length = Convert.ToDouble(Console.ReadLine());
         Console.WriteLine("Enter Width: ");
         width = Convert.ToDouble(Console.ReadLine());
      }
      public double GetArea() {
         return length * width;
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.Acceptdetails();
         r.Display();
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Enter Length:
4.4
Enter Width:
3.3
Length: 4.4
Width: 3.3
Area: 14.52

In the preceding example, the member variables length and width are declared private, so they cannot be accessed from the function Main(). The member functions AcceptDetails() and Display() can access these variables. Since the member functions AcceptDetails() and Display() are declared public, they can be accessed from Main() using an instance of the Rectangle class, named r.

Protected Access Specifier

Protected access specifier allows a child class to access the member variables and member functions of its base class. This way it helps in implementing inheritance. We will discuss this in more details in the inheritance chapter.

Internal Access Specifier

Internal access specifier allows a class to expose its member variables and member functions to other functions and objects in the current assembly. In other words, any member with internal access specifier can be accessed from any class or method defined within the application in which the member is defined.

The following program illustrates this −Live Demo

using System;

namespace RectangleApplication {
   class Rectangle {
      //member variables
      internal double length;
      internal double width;
      
      double GetArea() {
         return length * width;
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }//end class Rectangle
   
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.length = 4.5;
         r.width = 3.5;
         r.Display();
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 3.5
Area: 15.75

In the preceding example, notice that the member function GetArea() is not declared with any access specifier. Then what would be the default access specifier of a class member if we don’t mention any? It is private.

Protected Internal Access Specifier

The protected internal access specifier allows a class to hide its member variables and member functions from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.

C# Loops

There may be a situation, when you need to execute a block of code several number of times. In general, the statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

Programming languages provide various control structures that allow for more complicated execution paths.

A loop statement allows us to execute a statement or a group of statements multiple times and following is the general from of a loop statement in most of the programming languages −

Loop Architecture

C# provides following types of loop to handle looping requirements. Click the following links to check their detail.

Sr.No.Loop Type & Description
1while loopIt repeats a statement or a group of statements while a given condition is true. It tests the condition before executing the loop body.
2for loopIt executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.
3do…while loopIt is similar to a while statement, except that it tests the condition at the end of the loop body
4nested loopsYou can use one or more loop inside any another while, for or do..while loop.

Loop Control Statements

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

C# provides the following control statements. Click the following links to check their details.

Sr.No.Control Statement & Description
1break statementTerminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch.
2continue statementCauses the loop to skip the remainder of its body and immediately retest its condition prior to reiterating.

Infinite Loop

A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the for loop are required, you can make an endless loop by leaving the conditional expression empty.

Example

using System;

namespace Loops {
   class Program {
      static void Main(string[] args) {
         for (; ; ) {
            Console.WriteLine("Hey! I am Trapped");
         }
      }
   }
} 

When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but programmers more commonly use the for(;;) construct to signify an infinite loop.

C# – Decision Making

Decision making structures requires the programmer to specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages −

Decision making statements in C#

C# provides following types of decision making statements. Click the following links to check their detail.

Sr.No.Statement & Description
1if statementAn if statement consists of a boolean expression followed by one or more statements.
2if…else statementAn if statement can be followed by an optional else statement, which executes when the boolean expression is false.
3nested if statementsYou can use one if or else if statement inside another if or else if statement(s).
4switch statementswitch statement allows a variable to be tested for equality against a list of values.
5nested switch statementsYou can use one switch statement inside another switch statement(s).

The ? : Operator

We have covered conditional operator ? : in previous chapter which can be used to replace if…else statements. It has the following general form −

Exp1 ? Exp2 : Exp3;

Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.

The value of a ? expression is determined as follows: Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ? expression. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.

C# Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C# has rich set of built-in operators and provides the following type of operators −

  • Arithmetic Operators
  • Relational Operators
  • Logical Operators
  • Bitwise Operators
  • Assignment Operators
  • Misc Operators

This tutorial explains the arithmetic, relational, logical, bitwise, assignment, and other operators one by one.

Arithmetic Operators

Following table shows all the arithmetic operators supported by C#. Assume variable A holds 10 and variable B holds 20 then −

Show Examples

OperatorDescriptionExample
+Adds two operandsA + B = 30
Subtracts second operand from the firstA – B = -10
*Multiplies both operandsA * B = 200
/Divides numerator by de-numeratorB / A = 2
%Modulus Operator and remainder of after an integer divisionB % A = 0
++Increment operator increases integer value by oneA++ = 11
Decrement operator decreases integer value by oneA– = 9

Relational Operators

Following table shows all the relational operators supported by C#. Assume variable A holds 10 and variable B holds 20, then −

Show Examples

OperatorDescriptionExample
==Checks if the values of two operands are equal or not, if yes then condition becomes true.(A == B) is not true.
!=Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.(A != B) is true.
>Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.(A > B) is not true.
<Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.(A < B) is true.
>=Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.(A >= B) is not true.
<=Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.(A <= B) is true.

Logical Operators

Following table shows all the logical operators supported by C#. Assume variable A holds Boolean value true and variable B holds Boolean value false, then −

Show Examples

OperatorDescriptionExample
&&Called Logical AND operator. If both the operands are non zero then condition becomes true.(A && B) is false.
||Called Logical OR Operator. If any of the two operands is non zero then condition becomes true.(A || B) is true.
!Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.!(A && B) is true.

Bitwise Operators

Bitwise operator works on bits and perform bit by bit operation. The truth tables for &, |, and ^ are as follows −

pqp & qp | qp ^ q
00000
01011
11110
10011

Assume if A = 60; and B = 13; then in the binary format they are as follows −

A = 0011 1100

B = 0000 1101

——————-

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A  = 1100 0011

The Bitwise operators supported by C# are listed in the following table. Assume variable A holds 60 and variable B holds 13, then −

Show Examples

OperatorDescriptionExample
&Binary AND Operator copies a bit to the result if it exists in both operands.(A & B) = 12, which is 0000 1100
|Binary OR Operator copies a bit if it exists in either operand.(A | B) = 61, which is 0011 1101
^Binary XOR Operator copies the bit if it is set in one operand but not both.(A ^ B) = 49, which is 0011 0001
~Binary Ones Complement Operator is unary and has the effect of ‘flipping’ bits.(~A ) = -61, which is 1100 0011 in 2’s complement due to a signed binary number.
<<Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.A << 2 = 240, which is 1111 0000
>>Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.A >> 2 = 15, which is 0000 1111

Assignment Operators

There are following assignment operators supported by C# −

Show Examples

OperatorDescriptionExample
=Simple assignment operator, Assigns values from right side operands to left side operandC = A + B assigns value of A + B into C
+=Add AND assignment operator, It adds right operand to the left operand and assign the result to left operandC += A is equivalent to C = C + A
-=Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operandC -= A is equivalent to C = C – A
*=Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operandC *= A is equivalent to C = C * A
/=Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operandC /= A is equivalent to C = C / A
%=Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operandC %= A is equivalent to C = C % A
<<=Left shift AND assignment operatorC <<= 2 is same as C = C << 2
>>=Right shift AND assignment operatorC >>= 2 is same as C = C >> 2
&=Bitwise AND assignment operatorC &= 2 is same as C = C & 2
^=bitwise exclusive OR and assignment operatorC ^= 2 is same as C = C ^ 2
|=bitwise inclusive OR and assignment operatorC |= 2 is same as C = C | 2

Miscellaneous Operators

There are few other important operators including sizeof, typeof and ? : supported by C#.

Show Examples

OperatorDescriptionExample
sizeof()Returns the size of a data type.sizeof(int), returns 4.
typeof()Returns the type of a class.typeof(StreamReader);
&Returns the address of an variable.&a; returns actual address of the variable.
*Pointer to a variable.*a; creates pointer named ‘a’ to a variable.
? :Conditional ExpressionIf Condition is true ? Then value X : Otherwise value Y
isDetermines whether an object is of a certain type.If( Ford is Car) // checks if Ford is an object of the Car class.
asCast without raising an exception if the cast fails.Object obj = new StringReader(“Hello”);StringReader r = obj as StringReader;

Operator Precedence in C#

Operator precedence determines the grouping of terms in an expression. This affects evaluation of an expression. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator.

For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so the first evaluation takes place for 3*2 and then 7 is added into it.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators are evaluated first.

Show Examples

CategoryOperatorAssociativity
Postfix() [] -> . ++ – –Left to right
Unary+ – ! ~ ++ – – (type)* & sizeofRight to left
Multiplicative* / %Left to right
Additive+ –Left to right
Shift<< >>Left to right
Relational< <= > >=Left to right
Equality== !=Left to right
Bitwise AND&Left to right
Bitwise XOR^Left to right
Bitwise OR|Left to right
Logical AND&&Left to right
Logical OR||Left to right
Conditional?:Right to left
Assignment= += -= *= /= %=>>= <<= &= ^= |=Right to left
Comma,Left to right

C# Constants And Literals

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer Literals

An integer literal can be a decimal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, and there is no prefix id for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals −

212         /* Legal */
215u        /* Legal */
0xFeeL      /* Legal */

Following are other examples of various types of Integer literals −

85         /* decimal */
0x4b       /* hexadecimal */
30         /* int */
30u        /* unsigned int */
30l        /* long */
30ul       /* unsigned long */

Floating-point Literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

Here are some examples of floating-point literals −

3.14159       /* Legal */
314159E-5F    /* Legal */
510E          /* Illegal: incomplete exponent */
210f          /* Illegal: no decimal or exponent */
.e55          /* Illegal: missing integer or fraction */

While representing in decimal form, you must include the decimal point, the exponent, or both; and while representing using exponential form you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Character Constants

Character literals are enclosed in single quotes. For example, ‘x’ and can be stored in a simple variable of char type. A character literal can be a plain character (such as ‘x’), an escape sequence (such as ‘\t’), or a universal character (such as ‘\u02C0’).

There are certain characters in C# when they are preceded by a backslash. They have special meaning and they are used to represent like newline (\n) or tab (\t). Here, is a list of some of such escape sequence codes −

Escape sequenceMeaning
\\\ character
\’‘ character
\”” character
\?? character
\aAlert or bell
\bBackspace
\fForm feed
\nNewline
\rCarriage return
\tHorizontal tab
\vVertical tab
\xhh . . .Hexadecimal number of one or more digits

Following is the example to show few escape sequence characters −Live Demo

using System;

namespace EscapeChar {
   class Program {
      static void Main(string[] args) {
         Console.WriteLine("Hello\tWorld\n\n");
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Hello   World

String Literals

String literals or constants are enclosed in double quotes “” or with @””. A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.

You can break a long line into multiple lines using string literals and separating the parts using whitespaces.

Here are some examples of string literals. All the three forms are identical strings.

"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
@"hello dear"

Defining Constants

Constants are defined using the const keyword. Syntax for defining a constant is −

const <data_type> <constant_name> = value;

The following program demonstrates defining and using a constant in your program −Live Demo

using System;

namespace DeclaringConstants {
   class Program {
      static void Main(string[] args) {
         const double pi = 3.14159;   
            
         // constant declaration 
         double r;
         Console.WriteLine("Enter Radius: ");
         r = Convert.ToDouble(Console.ReadLine());
            
         double areaCircle = pi * r * r;
         Console.WriteLine("Radius: {0}, Area: {1}", r, areaCircle);
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Enter Radius: 
3
Radius: 3, Area: 28.27431

C# – Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C# has a specific type, which determines the size and layout of the variable’s memory the range of values that can be stored within that memory and the set of operations that can be applied to the variable.

The basic value types provided in C# can be categorized as −

TypeExample
Integral typessbyte, byte, short, ushort, int, uint, long, ulong, and char
Floating point typesfloat and double
Decimal typesdecimal
Boolean typestrue or false values, as assigned
Nullable typesNullable data types

C# also allows defining other value types of variable such as enum and reference types of variables such as class, which we will cover in subsequent chapters.

Defining Variables

Syntax for variable definition in C# is −

<data_type> <variable_list>;

Here, data_type must be a valid C# data type including char, int, float, double, or any user-defined data type, and variable_list may consist of one or more identifier names separated by commas.

Some valid variable definitions are shown here −

int i, j, k;
char c, ch;
float f, salary;
double d;

You can initialize a variable at the time of definition as −

int i = 100;

Initializing Variables

Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is −

variable_name = value;

Variables can be initialized in their declaration. The initializer consists of an equal sign followed by a constant expression as −

<data_type> <variable_name> = value;

Some examples are −

int d = 3, f = 5;    /* initializing d and f. */
byte z = 22;         /* initializes z. */
double pi = 3.14159; /* declares an approximation of pi. */
char x = 'x';        /* the variable x has the value 'x'. */

It is a good programming practice to initialize variables properly, otherwise sometimes program may produce unexpected result.

The following example uses various types of variables −Live Demo

using System;

namespace VariableDefinition {
   class Program {
      static void Main(string[] args) {
         short a;
         int b ;
         double c;

         /* actual initialization */
         a = 10;
         b = 20;
         c = a + b;
         Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c);
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

a = 10, b = 20, c = 30

Accepting Values from User

The Console class in the System namespace provides a function ReadLine() for accepting input from the user and store it into a variable.

For example,

int num;
num = Convert.ToInt32(Console.ReadLine());

The function Convert.ToInt32() converts the data entered by the user to int data type, because Console.ReadLine() accepts the data in string format.

Lvalue and Rvalue Expressions in C#

There are two kinds of expressions in C# −

  • lvalue − An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.
  • rvalue − An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Variables are lvalues and hence they may appear on the left-hand side of an assignment. Numeric literals are rvalues and hence they may not be assigned and can not appear on the left-hand side. Following is a valid C# statement −

int g = 20;

But following is not a valid statement and would generate compile-time error −

10 = 20;

C# Type Conversion

Type conversion is converting one type of data to another type. It is also known as Type Casting. In C#, type casting has two forms −

  • Implicit type conversion − These conversions are performed by C# in a type-safe manner. For example, are conversions from smaller to larger integral types and conversions from derived classes to base classes.
  • Explicit type conversion − These conversions are done explicitly by users using the pre-defined functions. Explicit conversions require a cast operator.

The following example shows an explicit type conversion

using System;

namespace TypeConversionApplication {
   class ExplicitConversion {
      static void Main(string[] args) {
         double d = 5673.74; 
         int i;
         
         // cast double to int.
         i = (int)d;
         Console.WriteLine(i);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

5673

C# Type Conversion Methods

C# provides the following built-in type conversion methods −

Sr.No.Methods & Description
1ToBooleanConverts a type to a Boolean value, where possible.
2ToByteConverts a type to a byte.
3ToCharConverts a type to a single Unicode character, where possible.
4ToDateTimeConverts a type (integer or string type) to date-time structures.
5ToDecimalConverts a floating point or integer type to a decimal type.
6ToDoubleConverts a type to a double type.
7ToInt16Converts a type to a 16-bit integer.
8ToInt32Converts a type to a 32-bit integer.
9ToInt64Converts a type to a 64-bit integer.
10ToSbyteConverts a type to a signed byte type.
11ToSingleConverts a type to a small floating point number.
12ToStringConverts a type to a string.
13ToTypeConverts a type to a specified type.
14ToUInt16Converts a type to an unsigned int type.
15ToUInt32Converts a type to an unsigned long type.
16ToUInt64Converts a type to an unsigned big integer.

The following example converts various value types to string type −Live Demo

using System;

namespace TypeConversionApplication {
   class StringConversion {
      static void Main(string[] args) {
         int i = 75;
         float f = 53.005f;
         double d = 2345.7652;
         bool b = true;

         Console.WriteLine(i.ToString());
         Console.WriteLine(f.ToString());
         Console.WriteLine(d.ToString());
         Console.WriteLine(b.ToString());
         Console.ReadKey();
            
      }
   }
}

When the above code is compiled and executed, it produces the following result −

75
53.005
2345.7652
True

C# – Data Types

The variables in C#, are categorized into the following types −

  • Value types
  • Reference types
  • Pointer types

Value Type

Value type variables can be assigned a value directly. They are derived from the class System.ValueType.

The value types directly contain data. Some examples are int, char, and float, which stores numbers, alphabets, and floating point numbers, respectively. When you declare an int type, the system allocates memory to store the value.

The following table lists the available value types in C# 2010 −

TypeRepresentsRangeDefault Value
boolBoolean valueTrue or FalseFalse
byte8-bit unsigned integer0 to 2550
char16-bit Unicode characterU +0000 to U +ffff‘\0’
decimal128-bit precise decimal values with 28-29 significant digits(-7.9 x 1028 to 7.9 x 1028) / 100 to 280.0M
double64-bit double-precision floating point type(+/-)5.0 x 10-324 to (+/-)1.7 x 103080.0D
float32-bit single-precision floating point type-3.4 x 1038 to + 3.4 x 10380.0F
int32-bit signed integer type-2,147,483,648 to 2,147,483,6470
long64-bit signed integer type-9,223,372,036,854,775,808 to 9,223,372,036,854,775,8070L
sbyte8-bit signed integer type-128 to 1270
short16-bit signed integer type-32,768 to 32,7670
uint32-bit unsigned integer type0 to 4,294,967,2950
ulong64-bit unsigned integer type0 to 18,446,744,073,709,551,6150
ushort16-bit unsigned integer type0 to 65,5350

To get the exact size of a type or a variable on a particular platform, you can use the sizeof method. The expression sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine −Live Demo

using System;

namespace DataTypeApplication {
   class Program {
      static void Main(string[] args) {
         Console.WriteLine("Size of int: {0}", sizeof(int));
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Size of int: 4

Reference Type

The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.

In other words, they refer to a memory location. Using multiple variables, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are: objectdynamic, and string.

Object Type

The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. The object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.

object obj;
obj = 100; // this is boxing

Dynamic Type

You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at run-time.

Syntax for declaring a dynamic type is −

dynamic <variable_name> = value;

For example,

dynamic d = 20;

Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.

String Type

The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.

For example,

String str = "Tutorials Point";

A @quoted string literal looks as follows −

@"Tutorials Point";

The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.

Pointer Type

Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as the pointers in C or C++.

Syntax for declaring a pointer type is −

type* identifier;

For example,

char* cptr;
int* iptr;

We will discuss pointer types in the chapter ‘Unsafe Codes’.

C# – Basic Syntax

C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, are said to be in the same class.

For example, let us consider a Rectangle object. It has attributes such as length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating the area, and displaying details.

Let us look at implementation of a Rectangle class and discuss C# basic syntax:

using System;

namespace RectangleApplication {
   class Rectangle {
      
      // member variables
      double length;
      double width;
      
      public void Acceptdetails() {
         length = 4.5;    
         width = 3.5;
      }
      public double GetArea() {
         return length * width; 
      }
      public void Display() {
         Console.WriteLine("Length: {0}", length);
         Console.WriteLine("Width: {0}", width);
         Console.WriteLine("Area: {0}", GetArea());
      }
   }
   class ExecuteRectangle {
      static void Main(string[] args) {
         Rectangle r = new Rectangle();
         r.Acceptdetails();
         r.Display();
         Console.ReadLine(); 
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 3.5
Area: 15.75

The using Keyword

The first statement in any C# program is

using System;

The using keyword is used for including the namespaces in the program. A program can include multiple using statements.

The class Keyword

The class keyword is used for declaring a class.

Comments in C#

Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below −

/* This program demonstrates
The basic syntax of C# programming 
Language */

Single-line comments are indicated by the ‘//’ symbol. For example,

}//end class Rectangle    

Member Variables

Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width.

Member Functions

Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetailsGetArea and Display.

Instantiating a Class

In the preceding program, the class ExecuteRectangle contains the Main() method and instantiates the Rectangle class.

Identifiers

An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in C# are as follows −

  • A name must begin with a letter that could be followed by a sequence of letters, digits (0 – 9) or underscore. The first character in an identifier cannot be a digit.
  • It must not contain any embedded space or symbol such as? – + ! @ # % ^ & * ( ) [ ] { } . ; : ” ‘ / and \. However, an underscore ( _ ) can be used.
  • It should not be a C# keyword.

C# – Program structure

Before we study basic building blocks of the C# programming language, let us look at a bare minimum C# program structure so that we can take it as a reference in upcoming chapters.

Creating Hello World Program

A C# program consists of the following parts −

  • Namespace declaration
  • A class
  • Class methods
  • Class attributes
  • A Main method
  • Statements and Expressions
  • Comments

Let us look at a simple code that prints the words “Hello World”

using System;

namespace HelloWorldApplication {
   class HelloWorld {
      static void Main(string[] args) {
         /* my first program in C# */
         Console.WriteLine("Hello World");
         Console.ReadKey();
      }
   }
}

When this code is compiled and executed, it produces the following result −

Hello World

Let us look at the various parts of the given program −

  • The first line of the program using System; – the using keyword is used to include the System namespace in the program. A program generally has multiple using statements.
  • The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld.
  • The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally contain multiple methods. Methods define the behavior of the class. However, the HelloWorld class has only one method Main.
  • The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class does when executed.
  • The next line /*…*/ is ignored by the compiler and it is put to add comments in the program.
  • The Main method specifies its behavior with the statement Console.WriteLine(“Hello World”);WriteLine is a method of the Console class defined in the System namespace. This statement causes the message “Hello, World!” to be displayed on the screen.
  • The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET.

It is worth to note the following points −

  • C# is case sensitive.
  • All statements and expression must end with a semicolon (;).
  • The program execution starts at the Main method.
  • Unlike Java, program file name could be different from the class name.

Compiling and Executing the Program

If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps −

  • Start Visual Studio.
  • On the menu bar, choose File -> New -> Project.
  • Choose Visual C# from templates, and then choose Windows.
  • Choose Console Application.
  • Specify a name for your project and click OK button.
  • This creates a new project in Solution Explorer.
  • Write code in the Code Editor.
  • Click the Run button or press F5 key to execute the project. A Command Prompt window appears that contains the line Hello World.

You can compile a C# program by using the command-line instead of the Visual Studio IDE −

  • Open a text editor and add the above-mentioned code.
  • Save the file as helloworld.cs
  • Open the command prompt tool and go to the directory where you saved the file.
  • Type csc helloworld.cs and press enter to compile your code.
  • If there are no errors in your code, the command prompt takes you to the next line and generates helloworld.exe executable file.
  • Type helloworld to execute your program.
  • You can see the output Hello World printed on the screen.

C# – Environment

In this chapter, we will discuss the tools required for creating C# programming. We have already mentioned that C# is part of .Net framework and is used for writing .Net applications. Therefore, before discussing the available tools for running a C# program, let us understand how C# relates to the .Net framework.

The .Net Framework

The .Net framework is a revolutionary platform that helps you to write the following types of applications −

  • Windows applications
  • Web applications
  • Web services

The .Net framework applications are multi-platform applications. The framework has been designed in such a way that it can be used from any of the following languages: C#, C++, Visual Basic, Jscript, COBOL, etc. All these languages can access the framework as well as communicate with each other.

The .Net framework consists of an enormous library of codes used by the client languages such as C#. Following are some of the components of the .Net framework −

  • Common Language Runtime (CLR)
  • The .Net Framework Class Library
  • Common Language Specification
  • Common Type System
  • Metadata and Assemblies
  • Windows Forms
  • ASP.Net and ASP.Net AJAX
  • ADO.Net
  • Windows Workflow Foundation (WF)
  • Windows Presentation Foundation
  • Windows Communication Foundation (WCF)
  • LINQ

For the jobs each of these components perform, please see ASP.Net – Introduction, and for details of each component, please consult Microsoft’s documentation.

Integrated Development Environment (IDE) for C#

Microsoft provides the following development tools for C# programming −

  • Visual Studio 2010 (VS)
  • Visual C# 2010 Express (VCE)
  • Visual Web Developer

The last two are freely available from Microsoft official website. Using these tools, you can write all kinds of C# programs from simple command-line applications to more complex applications. You can also write C# source code files using a basic text editor, like Notepad, and compile the code into assemblies using the command-line compiler, which is again a part of the .NET Framework.

Visual C# Express and Visual Web Developer Express edition are trimmed down versions of Visual Studio and has the same appearance. They retain most features of Visual Studio. In this tutorial, we have used Visual C# 2010 Express.

You can download it from Microsoft Visual Studio. It gets installed automatically on your machine.

Note: You need an active internet connection for installing the express edition.

Writing C# Programs on Linux or Mac OS

Although the.NET Framework runs on the Windows operating system, there are some alternative versions that work on other operating systems. Mono is an open-source version of the .NET Framework which includes a C# compiler and runs on several operating systems, including various flavors of Linux and Mac OS. Kindly check Go Mono.

The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools for Linux developers. Mono can be run on many operating systems including Android, BSD, iOS, Linux, OS X, Windows, Solaris, and UNIX.

What is C# ?

C# is a simple, modern, general-purpose, object-oriented programming language developed by Microsoft within its .NET initiative led by Anders Hejlsberg.

C# is designed for Common Language Infrastructure (CLI), which consists of the executable code and runtime environment that allows use of various high-level languages on different computer platforms and architectures.

The following reasons make C# a widely used professional language −

  • It is a modern, general-purpose programming language
  • It is object oriented.
  • It is component oriented.
  • It is easy to learn.
  • It is a structured language.
  • It produces efficient programs.
  • It can be compiled on a variety of computer platforms.
  • It is a part of .Net Framework.

Although C# constructs closely follow traditional high-level languages, C and C++ and being an object-oriented programming language. It has strong resemblance with Java, it has numerous strong programming features that make it endearing to a number of programmers worldwide.

Following is the list of few important features of C# −

  • Boolean Conditions
  • Automatic Garbage Collection
  • Standard Library
  • Assembly Versioning
  • Properties and Events
  • Delegates and Events Management
  • Easy-to-use Generics
  • Indexers
  • Conditional Compilation
  • Simple Multithreading
  • LINQ and Lambda Expressions
  • Integration with Windows

Sve što trebaš znati prije kupovine polaroid fotoaparata

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Instant fotoaparati postaju sve popularniji među mlađim generacijama. Iako danas možemo okinuti 500 kvalitetnih fotografija sa svojim mobitelom i odmah ih prikačiti na društvene mreže, postoji nešto posebno u automatskom ispisu fotografija koje ti omogućuju instant (Polaroid) kamere.

Dakle u minuti možeš imati fotografiju u fizičkom obliku u svojim rukama. Svi ostali fotoaparati, mobiteli i drugi uređaji za slikanje zahtijevaju i poseban uređaj za print fotografija. S instant kamerama, dobit ćeš all in one.

Instant fotoaparati često se nazivaju i Polaroid fotoaparatima ili kamerama, ali to je iz razloga što je Polaroid najpoznatija marka instant kamera pa su ljudi poistovjetili jedno s drugim. Nešto kao Kindle kod e-čitača knjiga. Međutim, Polaroid nije jedini proizvođač instant fotoaparata o čemu više u nastavku teksta.

Za korištenje instant fotoaparata trebat će ti i instant papir na koji će se slika printati. Svaki proizvođač koristi svoj papir/film i on je određen za točno određeni model fotoaparata. Tek kada u fotoaparat postaviš ispravan film, možeš početi slikati i printati fotografije.

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Glavne prednosti instant kamera

U svijetu DSLR fotoaparata, vrhunskih kamera na mobitelima i svih ostalih čuda tehnologije, instant kamere moraju ponuditi nešto što će ih izdvojiti iz mase i natjerati ljude ih kupe makar imaju smanjenu kvalitetu samih fotografija.

Jednostavnost korištenja

Jednostavnost korištenja je definitivno najveći plus koji Polaroid fotoaparati imaju nad ostalim modelima. Sve stane u jedan pritisak gumba i to je to. Njih će podjednako lako koristiti i mladi i stari. 

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Instant slika

Uz pametne telefone, navikli smo da sve fotke odmah pogledamo pa ih i podijelimo sa svima poznatima i nepoznatima na Facebooku, Instagramu i ostalim društvenim mrežama. Međutim, nekada sliku baš želimo odmah u fizičkom obliku kao vječnu uspomenu na snimljeni trenutak. Instant kamere omogućuju ti baš to.

Posebno iskustvo

Na stranu kvaliteta koju ti nude profesionalni aparati, razni filteri, trostruke kamere i sve ostalo što je postalo svakodnevnica u svijetu fotografije. Instant fotoaparati pružaju ti ipak neko drugačije, posebno iskustvo. Povratak u prošlost s velikim osmijehom na licu.

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Složili smo odlično gaming računalo za 6000 kn

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Moćna gaming računala znaju stajati i više od 10.000 kuna. Međutim, ako se malo potrudiš, odličan gaming PC možeš složiti i za puno manju cijenu. Mi smo se zato potrudili sastaviti gaming računalo za 6000 kuna kojeg ćeš bez problema moći koristiti sljedećih nekolika godina. 

To bi bilo naše gaming računalo koje će bez problema pokretati i najnovije naslove u punoj kvaliteti. Svakako uzmi u obzir da u ovu cijenu nije uključen monitor kao niti periferija (gaming miš, tipkovnica). S obzirom da je cijena ispod 6000 kn, taj iznos može izdvojiti za slaganje računala, ako sam nisi dovoljno stručan u tom polju. 

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Naše odlično gaming računalo ispod 6000 kn sastoji se od: 

  • AMD Ryzen 5 2600X – 1159 kn
  • MSI B450M PRO-M2 – 555 kn
  • Gigabyte GeForce GTX 1660 GAMING OC 6GB – 2064 kn
  • Corsair Vengeance LPX 16GB – 619 kn
  • Samsung SSD 860 EVO 500 GB – 572 kn
  • Phanteks Eclipse P400 – 386 kn
  • Corsair CX-550W- 519 kn

Ukupna cijena računala je 5874 kn. Napominjemo da su cijene izražene u članku formirane na dan pisanja članka i tijekom vremena se mogu mijenjati. 

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Što je DVB-T2 ?

DVB-T2 je TV signal koji se koristi za emitiranje nacionalnih, regionalnih i lokalnih televizijskih programa u zemaljskom odašiljanju, i to u poboljšanoj HD rezoluciji. Iako je signal probno dostupan zadnjih godinu dana, 27.10. kreće se službeni prijelaz koji će se odvijati do 12.11. po digitalnim regijama.

Nakon prelaska, u mreži multipleksa M1 odašiljat će se HRT 1 HD, HRT 2 HD, RTL HD, Nova TV HD, HRT 3 HD, HRT 4 HD, RTL 2 HD i Doma TV HD dok će se u multipleksu M2 odašiljati RTL kockica HD, CMC HD, Sportska televizija HD te postojeći regionalni programi.

Da bi mogao primiti DVB-T2 signal, potrebno je posjedovati standardnu antenu koja se i do sada koristila za prijem signala, kao i televizor ili digitalni prijemnik koji podržavaju DVB-T2 s HEVC/H.265 sažimanjem. U slučaju da tvoj televizor nema mogućnost primanja ovog signala, a nemaš niti odgovarajući digitalni prijemnik, više nećeš moći gledati niti jedan zemaljski TV program.

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VPN za početnike: kako sigurno surfati internetom i pristupiti sadržajima neovisno o geolokaciji

VPN ili virtualna privatna mreža je vrsta softvera koji mijenja tvoju IP adresu i šifrira tvoj internetski promet.

Time dobivaš viši stupanj zaštite i privatnosti dok surfaš internetom te možeš pristupiti sadržajima koje su blokirali davatelji internetskih usluga, vlade ili bilo koje druge organizacije ili osobe.

Šifriraj svoj internet promet i surfaj internetom bez imalo brige.

Da bi se spojio na VPN, moraš imati pružatelja internet usluga (T-Com, Iskon, B-net itd.). Kada pokreneš VPN aplikaciju, ona se povezuje na VPN server koji koristi pružatelj VPN usluge na koju si se pretplatio. Time se stvara tunel za informacije koji zaobilazi tvojeg pružatelja internet usluga i tako tvoj pružatelj internet usluga ne može vidjeti što radiš online, a web stranice koje posjećuješ ne mogu znati tko si.

VPN onemogućava tvojem pružatelju internet usluga da vidi što pretražuješ na internetu. Primjerice, ako skidaš piratske sadržaje, ne moraš brinuti da će tvoj internet provider te informacije proslijediti nadležnim institucijama.

VPN također pruža dodatnu razinu zaštite kada plaćaš online karticama, pa potencijalni hakeri ne mogu presresti te podatke. Sigurnost se odnosi i na sve lozinke, emailove, poruke i slične osjetljive informacije koje šalješ internetom. Možeš se spojiti na bilo koji javni WiFi (u kafiću, javnom prijevozu, šoping centrima, gradskim hotspotovima itd.), a VPN će sakriti tvoje osjetljive podatke od onih koji ih žele zloupotrijebiti ili ukrasti.

Jedan od popularnih razloga zašto se ljudi odluče pretplatiti na VPN usluge je mogućnost pristupa svim uslugama streaminga koje su blokirane u njihovoj zemlji. Primjerice, možeš gledati američki Netflix koji ima puno veću ponudu nego kod nas, možeš slušati najveću ponudu glazbe na Spotifyju, a također ti se više neće dogoditi da neki YouTube video nije dostupan u tvojoj zemlji.

Budući da VPN mijenja tvoju IP adresu, to oglašivačima jako otežava ciljano prikazivanje oglasa. To znači da ako jedan dan naručiš tenisice za trčanje, nećeš  morati gledati reklame tenisica na apsolutno svim oglasima koji ti se prikažu narednih 3 mjeseca.

VPN je odličan u borbi protiv cenzure, bilo da živiš u državi s opresivnom vladom ili su administratori u tvojoj studentskoj knjižnici ili u uredu zabranili pristup određenim stranicama.

Što je 5G i kako se koristi za prenošenje podataka

5G je nova, peta generacija mobilnih telekomunikacijskih mreža s pripadajućom infrastrukturom i uređajima. Temelji se na novim tehnologijama poput 5G New Radio (NR) koja koristi milimetarski valni spektar te mnogo veće radio frekvencije (5G koristi 28 GHz, dok 4G koristi 700-2.500 MHz).

To omogućuje prijenos eksponencijalno više podatakaveće brzineveći broj povezanih uređaja i manju latenciju.

Rad postojećih mreža, primjerice 4G, možemo usporediti s radom reflektora koji osvijetle cijelo područje, pri čemu se gubi puno svjetla (odnosno signala) na područja na kojima nema uređaja.

5G New Radio i još jedna nova 5G tehnologija naziva Massive MIMO (eng. multiple input multiple output) omogućit će jednostavniji i učinkovitiji fokus mreže na uređaje te tako poboljšati pokrivenost, brzinu i kapacitet.

Smjena generacija mobilnih telekomunikacijskim mreža događa se otprilike svakih 10 godina. Tako se 1G pojavio u osamdesetima prošlog stoljeća, u devedesetima je došao 2G (koji se kod nas počeo implementirati tek nakon ratnih godina), u 2000.-ima prelazimo na 3G mrežu, a današnji standard 4G mreže uveden je početkom 2010.-ih i upravo njemu možemo zahvaliti razvoj i popularizaciju pametnih telefona.

4 načina kako zaštititi oči od ekrana

Osam sati dnevno provedeš gledajući u ekran računala na poslu? Nakon toga se i doma uhvatiš kako gledaš u ekran? Tvoje oči sve to trpe. S obzirom na to da živimo u svijetu u kojem odmak od ekrana gotovo da i nije moguć, a sav se posao odvija pomoću računala, izgleda da smo osuđeni na cjelodnevno gledanje u ekrane.

1. 20-20-20

Ovo pravilo najlakša je stvar koju možeš napraviti kako bi odmorio oči od naprezanja kojemu su izložene tijekom gledanja u ekran.

Pravilo 20-20-20 znači 20 minuta rada, 20 sekundi pauze, 20 minuta rada.

Tijekom pauze važno je da pogled usmjeriš negdje u daljinu, poželjno kroz prozor u jednu točku i 20 sekundi ostaneš s pogledom u daljinu.

Na taj će se način spriječiti blokada očiju kao posljedica konstantnog fokusiranja oka na ekran.

2. Trepći

U jednoj minuti prosječna osoba trepne 16 puta. Međutim, prilikom rada na računalu i gledanja u ekran taj se broj znatno smanjuje (do 5 puta). Treptanje je prirodna zaštita oka kojom tvoje oči dobivaju dovoljno vlage. Baš ono što oku kronično nedostaje prilikom gledanja u ekran.

Ako se već ne možeš natjerati na konstantno treptanje, druga je opcija korištenje umjetnih suza. U protivnom si osuđen na crvene i bolne oči.

3. Udaljenost od ekrana

Za umor očiju važna je i udaljenost na kojoj sjediš od ekrana. Pravila govore kako bi minimalna udaljenost morala biti u rasponu ispružene ruke. Znači kada ispružiš ruku ne smiješ njome dotaknuti ekran ili ekran postavi na udaljenosti između 50 i 80 cm.

4. Češće pauze

Iako će mnogi pomisliti kako će češće pauze imati negativan efekt na produktivnost, one imaju upravo kontra efekt.

Istraživanje provedeno od strane NIOSH-a (The National Institute for Occupational Safety and Health) pokazalo je kako su radnici koji su osim osnovnih pauza za ručak (30 min) i dvije pauze od 15 minuta, imali i 4 dodatne pauze od 5 minuta bili znatno produktivniji od svojih kolega.

Kako opremiti kućno kino – televizor ili projektor?

Odlučio si reći ne velikim kino dvoranama i uživati u udobnosti vlastitog kućnog kina? Sigurno si razmišljao o velikom OLED smart TV-u koji će pokriti pola zida i pružiti fenomenalnu sliku. Slažemo se s tom idejom, ali također imamo jedan malo drugačiji prijedlog – jesi li ikada razmišljao o ugradnji projektora i platna?

Projektor za kućno kino

Najveća prednost projektora je savršeno velika slika koju projicira. Iako ona može biti ograničena veličinom projekcijskog platna koji kupiš, u pravilu je i do nekoliko puta veća od najvećeg televizora kojeg si možeš priuštiti.

Užitak gledanja slike koja se proteže kroz čitavo vidno polje sigurno ti ne moramo dodatno objašnjavati.

Gledanje filmova, serija i utakmica, pa čak i igranje igrica, u takvom formatu potpuno je drugačije iskustvo nego naprezanje oči dok gledaš u mali ekran na drugom kraju prostorije. Detalji su uočljiviji, slika te uvuče u radnju i doživljaj je kao u pravom kinu.

Sve je to super kada se zabavljaš u večernjim i noćnim satima. Nažalost, danje svjetlo ponekad korištenje projektora čini skoro pa nemogućim. Projektor emitira takvu sliku da ju je moguće vidjeti samo u zamračenim prostorijama.

Ako kupiš najkvalitetniji projektor i kombiniraš ga s najkvalitetnijim projekcijskim platnom, jako danje svjetlo svejedno će isprati sliku. Ako ne želiš tijekom dana spuštati rolete i navlačiti zastore, nećeš moći istovremeno uživati u suncem okupanoj prostoriji i filmu na projektoru.

Dobri laptopi za srednjoškolce

Odgovarajući laptop za srednju školu malo je teže izabrati, baš zbog velike količine različitih usmjerenja, a samim time i različitih potreba po pitanju prijenosnih računala.

Sigurno je kako je laptop srednjoškolcima puno potrebniji nego osnovnoškolcima, a mi ćemo se i dalje držati popularne ‘koristit ću laptop za svašta po malo’ kategorije laptopa.

Držimo da će laptopi do 4000 kuna imati sve odgovarajuće specifikacije koje će srednjoškolcu trebati za njegovo obrazovanje. Ponovno će najveće pitanje biti oko SSD diska, ali kako je životni vijek jedna od njegovih glavnih prednosti, postoji opravdana mogućnost da će ga takav laptop služiti čak i po odlasku na fakultet.

SSD disk i veća količina RAM-a (8 GB) izgleda kao bolja kombinacija nego investiranje u bolji procesor koji će biti uparen s klasičnim tvrdim diskom i manjom količinom RAM-a. Napominjemo da i dalje pričamo o laptopima za školske potrebe, a ne za zabavu.

Dobar studentski laptop – kako ga izabrati

Koji laptop izabrati za koji fakultet?

Prije nego uopće krenemo u same karakteristike dobrog studentskog laptopa, važno je napomenuti da laptop uvijek biraš prema fakultetu kojeg pohađaš. Tehnički fakulteti zahtijevat će i moćnija prijenosna računala, dok će studentima humanističkih fakulteta i nešto slabiji laptopi biti dovoljni. Jasno ti je da isti laptop nije potreban osobi na pravnom fakultetu i onoj na FER-u. Čini se sasvim logično.

Kako velika većina studenata kroz cijelo studentsko razdoblje koristi jedan laptop, zahtjevi samog fakulteta trebali bi biti primarni u tvom izboru. Naravno, vodič za kupovinu laptopa prema svakom posebnom fakultetu ne možemo napraviti, ali zato smo sastavili sve najbitnije komponente koje bi studentski laptop trebao imati, a da svi studenti budu zadovoljni njime.

SSD disk je pravi prijatelj studentskog laptopa

SSD diskovi u laptopima su postali sve popularniji i to je nešto što bi trebao imati svaki studentski laptop. Oni donose brzinu i instant paljenje, pokretanje programa, a to je nešto što ćeš posebno cijeniti. Vremena kada si nakon pokretanja laptopa mogao otići skuhati kavu napokon su došla kraju, sada će ti laptop biti spreman za rad u samo par sekundi. Lijep je osjećaj kada na predavanju otvoriš laptop i on se odmah upali, a ne da potpuno funkcionalan postane taman na kraju predavanja.

SSD disk je i dugovječniji od klasičnog tvrdog diska, a to će dobro doći ako ne planiraš tijekom studiranja mijenjati laptop par puta. Ili ako ne planiraš studirati desetak godina.

Što se veličine tiče, uzmi onoliko koliko ti budžet dopušta. Vjerojatno će to biti 256 GB – standard kod srednjeg ranga laptopa. Znamo da ti se to čini malo jer na njega planiraš nakrcati svih 8 sezona Igre prijestolja, 12 sezona Teorije velikog praska i barem 45 Cinestar blockbustera (inače, srijedom imaš popuste, nije ni to tako strašno). Ali ako smatraš da nećeš imati dovoljno prostora za svoju multimediju, uzmi neki vanjski disk za 300-injak kuna i riješio si sve svoje životne probleme.

8 GB RAM 

8 GB RAM-a postao je gotovo pa standard pa ako nisi baš jako ograničen budžetom, svakako pronađi takav laptop. 8 GB RAM-a i SSD disk garancija su da će ti laptop raditi brzo i efikasno što će vjerojatno dovesti do toga da će tvoje učenje biti malo manje efikasno. Ali gle, negdje dobiješ, negdje izgubiš.

Ako si ipak kratak s budžetom, onda će i 4 GB RAM-a biti sasvim dobro. Pogotovo za studente kojima će laptop služiti za pretraživanje Wikipedije (i ne, Wikipedia nije relevantan izvor pri pisanju seminara i diplomskih radova), gledanje filmova i serija i puštanje glazbe kada se ekipa skupi da zajedno učite.

Plaće u Hrvatskoj iznad 10.000 HRK

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  1. C++ developer – 11.000 HRK
  2. DevOps engineer – 11.500 HRK
  3. Direktor prodaje – 13.500 HRK
  4. Full Stack developer – 14.000 HRK
  5. IT Consultant – 11.000 HRK
  6. Liječnik – 11.500 HRK
  7. Linux stručnjak – 12.500 HRK
  8. Product manager – 12.000 HRK
  9. Python developer – 12.500 HRK
  10. Revizor – 11.500 HRK
  11. Software engineer – 10.500 HRK
  12. Specijalist za kontroling – 13.000 HRK
  13. Sezonski šef kuhinje – 11.000 HRK
  14. Voditelj financija – 13.000 HRK
  15. Voditelj ITa – 11.000 HRK
  16. Voditelj IT projekata – 10.500 HRK
  17. Voditelj ljudskih resursa – 13.500 HRK
  18. Voditelj u ugostiteljstvu – 10.000 HRK
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Zašto auto zimi troši više goriva + savjeti za uštedu

Auto zimi više troši i s time se jednostavno moraš pomiriti.

Ništa što napraviš to neće promijeniti. Ne postoji 5 koraka do magične uštede. Međutim, postoje mali koraci koje možeš poduzeti kako bi razlika u potrošnji bila što manja, a sigurnost u vožnji veća.

Zašto je zimi veća potrošnja?

U zimskim mjesecima motor jače radi. Zbog niskih temperatura tekućine poput motornog ulja i ulja u mjenjaču su viskoznije nego inače te se povećava trenje.

Niske temperature smetaju akumulatoru i alternatoru, kojemu je potrebno više energije da puni akumulator.

Niske temperature smanjuju i tlak u gumama. Osim što se takve gume brže troše, također pružaju i veći otpor tijekom vožnje. Zbog toga motor mora više raditi i tako troši i više goriva.

Hladni zrak je gušći, a to smanjuje aerodinamičnost vozila. Ako još na vozilu imaš nosač koji ne koristiš, potrošnja goriva raste.

Jedna od navika koju svi imamo je puštanje auta da radi u leru 5-10 minuta kako bi se motor zagrijao. Međutim, to nije najbolja praksa. Možda će grijanje za to vrijeme ugrijati unutrašnjost auta, ali unutarnje grijanje i temperatura motora nisu ista stvar.

Naravno da ne želiš sjesti u hladan auto. Slobodno ga upali i okreni grijanje dok zastružeš led sa stakla. Ali zaista nema potrebe da radi na prazno 10 minuta, pogotovo jer ćeš motor prije ugrijati vožnjom.

Osim što će se motor auta prije zagrijati u vožnji, također će trošiti manje goriva nego dok radi u mjestu. 

Saznaj koja je osnovna DJ oprema

Odlučio si krenuti putem DJ velikana i osmisliti svoje ritmove za party mase? Imaš viška slobodnog vremena i htio bi stvarati nešto sebi za dušu? Ako planiraš zaploviti u DJ vode, provjerili smo koje su 3 osnovne stvari koje ti trebaju od opreme.

Danas temelj DJ opreme čine samo tri jednostavna uređaja – laptopkontroler slušalice.

Kontroler je najvažniji dio tvoje DJ opreme. Spaja se na laptop i omogućuje ti da oblikuješ zvuk i stvaraš efekte te tako glazbi dodaš svoj originalni potpis, a zamjenjuje tradicionalne dijelove set-upa poput vinila ili CD playera.

Laptop i kontroler omogućit će ti da, kada je stvaranje glazbe u pitanju, daš mašti na volju. No, da bi svoja remek djela doveo do savršenosti, trebat će ti par kvalitetnih slušalica. Kontroler možeš spojiti na bilo koji zvučni sustav, ali slušalice će ti omogućiti zvučnu kontrolu nad glazbom kakvu preko zvučnika ne možeš dobiti.

Nema potrebe da kupuješ najskuplje slušalice na tržištu, ali koncentriraj se na kvalitetne proizvođače jer kod slušalica je kvaliteta zvuka top prioritet. Slušalice također trebaju biti zatvorenog tipa preko ušiju tako da izoliraju vanjsku buku. To će ti omogućiti da se bolje fokusiraš na glazbu koja dolazi iz njih.

Ako želiš povećati fleksibilnost svojeg DJ setup-a, odličan način da to uradiš jest kupovina aktivnih zvučnika. Njih ne trebaš spajati na pojačalo, što znači da možeš sa sobom ponijeti svoju DJ opremu na bilo koje događanje i spreman si za hipnotiziranje party ekipe svojim DJ ritmovima.

Kako pojačati Wi-Fi signal

Upalio si stream najvažnije utakmice, a on šteka svakih nekoliko sekundi? Najnovija sezona Bridgertona je vani, a ti je ne možeš pogledati jer je internet preslab? Kada je najvažnije, signal puca; a tvoja je glava već napravila udubljenje u zidu od silnih udaraca? 

Kako ne bi glavom probio zid do susjeda i na kraju koristio njegovu bežičnu mrežu, vrijeme je da napraviš nekoliko brzih zahvata koji će pojačati tvoj Wi-Fi signal.

Prva stvar koju možeš napraviti je postaviti router na najbolje mjesto u svojem domu. Zvuči toliko jednostavno, a opet mnogi upravo zbog toga imaju velikih problema s prijemom signala. Zato te još jednom pitamo: imaš li router na najboljoj mogućoj poziciji? I sjeti se, nema glupih pitanja, samo glupih odgovora.

Kako signal usporavaju mnoge prepreke poput zidova, prozora, vrata, ogledala, namještaja itd., idealno bi bilo kada bi ruter bio udaljen od njih. Kako bi to značilo da će on lebdjeti na sredini sobe, jasno je kako to i nije moguće izvesti. 

Idealno bi bilo kada bi taj dio bio otvoren, primjerice hodnik ili otvorena dnevna soba, kako bi signal imao što manje smetnji. Smjestiš li router u zatvorenu sobu, već si mu na jedan način blokirao signal.

Kuće na kat također iziskuju posebno uređenje Wi-Fi mreže. Želiš li koristiti samo jedan router bez ikakvih pojačivača signala ili drugih rutera, postavi ga na gornji kat. Tako će signal bolje dopirati do prizemlja nego obrnuto. 

Zašto kupiti Android TV ?

Primili smo puno upita što je bolje izabrati – Smart TV ili Android TV? Iako razumijemo pitanje, važno je reći kako smart televizori i Android televizori nisu dvije različite stvari. Svaki Android televizor je ujedno i smart televizor, ali svaki smart televizor nije ujedno i Android televizor. 

Vjerojatno već znaš kako je Android u vlasništvu Googlea, pa se neke od prednosti naziru same po sebi. Android TV imat će najveću bazu aplikacija, a na njegov će Play Store aplikacije dolaziti najbrže. Google je kao mater iz TBF-ove pjesme, zna gdje radiš i di se krećeš. Samim time sigurno je kako će ti uvijek izbacivati najrelevantniji sadržaj prema tvojim interesima. A vjeruj, Google poznaje tvoje interese bolje i od tebe samog.

Moramo spomenuti da Google mijenja svoj Android TV u novi Google TV UI koji bi ti trebao nuditi još bolje sadržaje na tvojem početnom zaslonu.

Druga zgodna stvar kod Android TV-a je ta što on u sebi ima ugrađeni Chromecast pa ćeš u tren oka sadržaj sa svog Android mobitela ili tableta moći streamati na televizoru. Naravno, spojiti možeš i svoj laptop s televizorom, jedino što trebaš je Google Chrome u kojem pritisneš Cast to begin.

Ne treba ni reći da ćeš odmah imati pristup i najpopularnijim aplikacijama poput NetflixaYouTubea, Amazon Primea i mnogih drugih.

Kao i uvijek kada se radi o Androidu, problem može biti neujednačenost performansi, što ovisno o proizvođaču. Gotovo uvijek netko od proizvođača ubaci nešto svoje u operativni sustav kako bi se istaknuli, omogućili ‘bolje’ performanse ili nekog trećeg razloga. Nažalost, ponekad upravo zbog toga Android TV bude lagano nestabilan s čestim zamrzavanjima.

Android TV pronaći ćeš na popularnim televizorima kao što su Sony i Philips, a kako nije vezan direktno uz jednog proizvođača, tako niti izgled neće biti skroz identičan na različitim modelima.

5 zgodnih komada tehnologije iz Xiaomi svijeta

Krenulo je s pametnim telefonima, doživjelo vrhunac s električnim romobilima, a sada je kućno ime zahvaljujući lepezi korisnih pametnih proizvoda koji nam olakšavaju svakodnevicu. Naravno, govorimo o Xiaomiju, popularnom kineskom divu koji je pokazao da ne vrijedi uvijek ona stara “kol’ko para, tol’ko muzike”.

1. Bežični miš Xiaomi Mi Dual Mode Wireless Mouse Silent Edition

Elegantan, učinkovit i – tih! S ovim gotovo nečujnim mišem moći ćeš uživati u poslu bez ometanja. Osim što ga nećeš čuti, toliko je udoban, da ćeš imati osjećaj kao da je produžetak tvoje ruke.

Za rad koristi Bluetooth i WiFi tehnologiju, a da bi radio, trebaš njegov receiver uključiti u računalo te u samog miša staviti dvije AAA baterije. Mogu ga koristiti i ljevaci i dešnjaci, a ujedno možeš namjestiti i njegov DPI, koji inače ide do 1300, kako ti najbolje odgovara.

2. Prijenosni usisavač Mi Vacuum Cleaner Mini

Ovo je jedan od onih gadgeta za kojeg nisi ni znao da ti treba dok nisi vidio njegove neodoljive funkcionalnosti.

Malen, ali impresivan. S maksimalnom snagom usisavanja od 13 kPa, 88.000 okretaja motora u minuti te do 30 minuta standardnog usisavanja, odlična je nadopuna kućanskim pomagalima. Umjesto da vučeš glomazne aparate iz ormara ili, ne daj bože, koristiš metlicu i mišćaflin, ovaj mali stroj riješit će sve tvoje probleme. Reci zbogom mrvicama hrane u tastaturi jednom zauvijek!

3. Xiaomi Mi PRO 2 električni romobil

Gle, ne možeš očekivati da će lista zanimljivih Xiaomi proizvoda proći bez njihovih romobila. Jedan od naših kolega je upravo ovaj model upisao kao BMW među e-romobilima, a iako nećemo službeno podržati takav subjektivni stav, specifikacije kažu da se radi o pravoj bombi.

S motorom od 300W i baterijom od 12.800 mAh možeš proći do čak 45 km u jednom punjenju. Ima čak i E-ABS sustav, a u kupovini dobiješ i jednu rezervnu gumu.

4. Xiaomi Mi 20W bežični auto punjač

Ako već nemaš punjač za auto, pretpostavljamo da nemaš ni auto. Ako pak nisi zadovoljan punjačem kojeg imaš ili tražiš  punjač za svojeg novog limenog ljubimca, imamo pravu stvar za tebe.

Za mobitele koji podržavaju bežično punjenje tu je atraktivni Xiaomi Mi 20W bežični punjač. Kada njegovi senzori osjete da mu se približava mobitel, automatski će rastvoriti ručice i uhvatiti uređaj. Pa ti reci da to nije kul!

5. Xiaomi Mi Robot Builder

Ako imaš klince, ovo će ih oduševiti. Čak ako ih i nemaš, možeš kupiti unaprijed dok ih ne dobiješ čisto da testiraš ako sve radi kako spada i da se bolje upoznaš sa sigurnosnim aspektima igračke, kao svaki brižan roditelj.

Mi Robot Builder modularna je igračka za kodiranje koja se može sastaviti u različite strukture pomoću 978 blokova igračaka zajedno s ostalim dijelovima poput kotača, zupčanika i lanaca. Robotom se potom upravlja pametnim telefonom. I, kad ga naručuješ?

Zaboravi na loš zvuk televizora uz ovo jednostavno rješenje – soundbar!

Ako ti se ne sviđa zvuk tvojeg televizora, a ne želiš ulagati u sustav kućnog kina, vrijeme je jednostavno rješenje. Donosimo ti 7 stvari za znati prije kupovine soundbara.

Jedno moramo odmah raščistiti – soundbar nije i nikada neće biti adekvatna zamjena pravim zvučnicima. Iako postoje modeli vrhunske kvalitete, većina soundbara ipak je svega nekoliko razina iznad zvučnika tvojeg TV-a. 

Soundbar je namijenjen korisnicima koji žele kvalitetniji zvuk od onog s njihovog televizora, a ne treba im cijeli 5.1 ili 7.1 sustav zvučnika.

Problem sa suvremenim televizorima je taj što postaju sve tanji, a to znači da u njima ima sve manje mjesta za kvalitetne drivere. Slika je fenomenalna, a zvuk k’o na radiju u staroj peglici.

Soundbar ne može biti jednostavniji – izvadiš ga iz kutije, spojiš na televizor i odmah možeš uživati u poboljšanom zvuku. Nema žica, nema instalacija.

Stvar se svodi na ovo: ako želiš istinski doživljaj kućnog kina, tada je bolje da odabereš kompletan sustav zvučnika. Soundbar, koliko god kvalitetan bio, teško može zamijeniti zvučnike.

Postoje dvije vrste soundbara –  klasični soundbara u obliku poluge ili tzv. soundbase

Klasični soundbar duguljastog je oblika. Obično ga se postavlja ispred televizora, a može ga se montirati i na zid. Ovaj soundbar atraktivnog je izgleda, no može se dogoditi da blokira signal od televizora ako se nalazi ispred njega. 

Soundbase je u obliku kutije koju se stavlja ispod televizora. Odlično je rješenje ako imaš malo prostora na raspolaganju.

Očiti problem je veličina, odnosno težina televizora. Iako je ovakav soundbar robusniji i izdržljiviji upravo zbog svoje namjene da se televizor stavlja na njega, prije kupovine obavezno provjeri do koliko kilograma može izdržati. 

Ovakvi modeli soundbara često su većih dimenzija, a to znači da u njih stanu veći driveri. A veći driveri često znače i bolji zvuk.

Međutim, u stvarnom životu nemaš velikog izbora – soundbase prava je rijetkost i uglavnom ćeš birati između štapićastih zvučnika.

Također postoji aktivni pasivni soundbar.

Aktivni soundbar je onaj s početka priče – samo ga spojiš na televizor i spreman je za upotrebu. Pasivni soundbar više nalikuje tradicionalnom zvučniku, odnosno potrebno je spojiti ga na poseban receiver. 

5 PS4 igara koje ne možemo prestati igrati

Nakon napornog radnog dana želiš pobjeći u neke druge svjetove? Pustiti mozak na pašu, osjetiti malo adrenalina ili provesti vrijeme s prijateljima? Ovo je 5 PS4 igara koje su nam pomogle u tome. Provjeri je li i tvoja omiljena igra na popisu!

  1. Cyberpunk 2077

Cyberpunk 2077 je akcijska avanturistička priča. Mjesto radnje je Night City, megalopolis opsjednut s moći, glamurom i modifikacijama tijela. Igra se iz perspektive plaćenika V koji je u potrazi za ključem besmrtnosti u obliku jedinstvenog implantanta.

Što ovu igru čini posebnom? Ogroman svijet, odličan humor, pregršt RPG elemenata savršeno ukomponiranih u igru, prekrasna grafika, impresivno mnogo detalja… nemamo što drugo dodati osim da ćeš prevesti sate i sate zadubljen u ovaj cyberpunk svemir.

2. Shadow of the collosus

Stari klasik koji je nedavno doživio vizualni remake. Za razliku od Cyberpunka, ovdje nema svjetova za istraživanje. Umjesto toga, fokus je na borbi sa 12 Colossusa, ogromnih bića koje mladić Wander treba pobijediti u zabranjenoj zemlji kako bi oživio djevojku Mono.

Vrijeme ćeš provesti u potrazi za slabim točkama Colossusa te uživanju u dirljivoj priči koja će u tebi probuditi osjećaje za koje nisi znao da ih imaš.

3. The Last Of Us Part 2

Teško nam je zamisliti da imaš PS4, a da još nisi zaigrao The Last of Us. Da je ova igra hollywoodski film, bio bi ekstra popularan ljetni blockbuster koji bi srušio sve rekorde posjećenosti.

Kreativnost i improvizacija glavni su aduti pri prolasku kroz ovu šokantnu, zastrašujući i izuzetno dirljivu avanturu koja će ti se uvući pod kožu.

4. Call Of Duty – Black Ops 4

Za one koji će u ovu priču ući prvi put, igra može djelovati zbunjujuće. Što se točno događa, tko su sukobljene strane i tko su likovi s kojima se igra objašnjeno je u prethodnim iteracijama igre. Ako to sve već znaš, i tražiš dobru multiplayer pucačinu da zaigraš s ekipom, COD Black Ops bit će taman po tvojem ukusu.

5. Crash Bandicoot 4

Za kraj nešto malo lakše. Zabavna, dinamična i izuzetno pitka igra jednako će oduševiti iskusne PS4 igrače i početnike nižih uzrasta. Odlična je zabava kada želiš skratiti vrijeme, zaigrati s klincem, družiti se sa svojom boljom polovicom ili prisjetiti se sličnih igara koje si igrao kao mali.

Vesele boje, pregršt mapa za igranje, kratke i zabavne utrke i vježbanje refleksa garantiraju da ćeš se dobro osjećati.