Introduction : A extension methods is an important method of c#. An extension method is always used in a static class. It is parametric type. If you want to not create the object of a class and invoke the methods without a class object in this type situation we have to used the extension methods. In a extension methods we have invoke methods of a class to it's variable. The first variable of extension methods is always used of "this" keywords. The benefit of extension methods you have no need to create the object of a class and invoke of methods of class to it's variable.

Step 1 : Open Visual Studio 2010.

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Step 2 : In a window form add four buttons.

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Step 3 : In Solution Explorer right click and add a new class.
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Step 4 : Define the extension methods in a class.

code :

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

{
 static class manish
 {
public static int sum(this int a, int b)
{
int c = a + b;
return c;
}
public static int mul(this int a, int b)
{
int c = a * b;
return c;
}
public static int sub(this int a, int b)
{
int c = a - b;
return c;
}
public static int div(this int a, int b)
{
int c = a / b;
return c;
}
}
}

Step 5 : In window form Invoke a methods on button click event.

Code :

using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Data;
 using System.Drawing;
 using System.Linq;
 using System.Text;
 using System.Windows.Forms;
 namespace Extension_methods
{
public partial class Form1 : Form
 {
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{ int a = 10, b = 20;
int c= b.sum(a);
MessageBox.Show(c.ToString());
}
private void button2_Click(object sender, EventArgs e)
{
int a=20, b=30;
int c=b.sub(a);
MessageBox.Show(c.ToString());
}
private void button3_Click(object sender, EventArgs e)
{
int a = 100, b = 200;
int c = b.mul(a);
MessageBox.Show(c.ToString());
}
private void button4_Click(object sender, EventArgs e)
{
int a =5, b = 100;
int c = b.div(a);
MessageBox.Show(c.ToString());
}
}
}

Step 6 : Now Press F5 and run the application.

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Step 7 : Now we click in Button and find the output for all operation.

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