Two numbers swapping program without using third variable in c#.

using System;

class abc
{
    double a, b;
    public void swap()
    {
        Console.WriteLine("Program for swapping : ");
        Console.WriteLine("Numbers before swapping : ");
        Console.WriteLine("Enter first no : ");
        a = Convert.ToDouble(Console.ReadLine());
        Console.WriteLine("Enter second no : ");
        b = Convert.ToDouble(Console.ReadLine());
        a = a + b;
        b = a - b;
        a = a - b;
        Console.WriteLine("Numbers after swapping : ");
        Console.WriteLine("First no is : " + a);
        Console.WriteLine("Second no is : " + b);
        Console.ReadKey();
    }
}
class aa
{
    public static void Main(string[] args)
    {
        abc a = new abc();
        a.swap();
    }
}
Output: