swap two values without third variable

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace ConsoleApplication1

{

    public class swapClass 

    {

        // Swap without using third variable

        public void swapWTMethod(ref int a, ref int b)

        {

            a = a + b;

            b = a - b;

            a = a - b;         

        }

    }

    public class Program

    {

        static void Main(string[] args)

        {

            swapClass obj = new swapClass();

            int a=10;

            int b=20;

            Console.WriteLine("Before SwapWT A= " + a + " B =" + b);

            obj.swapWTMethod(ref a, ref b);

            Console.WriteLine("After SwapWT A= " + a + " B =" + b);

            Console.ReadLine();

        }

    }

}