call by reference.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace callByRefer

{

    class Program

    {

       public static void swap(ref int a, ref int b)

       {

           a = a + b;

           b = a - b;

           a = a - b;

           Console.WriteLine("after swapping value of a {0} and b {1}", a, b);

       }

       static void Main(string[] args)

       {

           int c = 10, d = 20;

           Console.WriteLine("before swapping  value of a {0} and b is{1}", c, d);

           swap(ref c, ref d);

       }

    }

}