Extension Method in C#

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.

• Go to file -> New->Projects.
• Open Windows Application Form.

Step 2 : In a window form add four buttons.

• Add
• Sub
• Mul
• Div

Step 3 : In Solution Explorer right click and add a new class.

• Solution Explorer->Right Click->Add ->New Item's-> add class.    
  

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.

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