How do you swap two numbers without using the third variable code example

Example 1: swap without using third variable

// SWAPPING WITHOUT USING THIRD VARIABLE
#include<stdio.h>  
 int main()    
{    
int a=10, b=20;      
printf("Before swap a=%d b=%d",a,b);      
a=a+b;//a=30 (10+20)    
b=a-b;//b=10 (30-20)    
a=a-b;//a=20 (30-10)    
printf("\nAfter swap a=%d b=%d",a,b);    
return 0;  
}

Example 2: swap 2 integers without using temporary variable

using System;

class MainClass {
  public static void Main (string[] args) {
    int num1 = int.Parse(Console.ReadLine());
    int num2 = int.Parse(Console.ReadLine());
      num1 = num1 + num2; 
      num2 = num1 - num2; 
      num1 = num1 - num2; 
      Console.WriteLine("After swapping: num1 = "+ num1 + ", num2 = " + num2); 
    Console.ReadLine();
  }
}