using System;

public class swap{

    public void change(ref int a, ref int b){

        int temp = a;

        a = b;

        b = temp;

    }

}

​

public class Program

{

    public static void Main()

    {

        int a = 10;

        int b = 20;

        swap sw = new swap();

        sw.change(ref a, ref b);

        Console.WriteLine("a : " + a);

        Console.WriteLine("b : " + b);

    }

}