C++ program swapping of two numbers without using 3rd variable

Do you know to swap using 3rd variable ?
If yes then learn who to swap without using 3rd variable

#include<iostream>

using namespace std;

void main()

{

//Swapping without 3rd variable

 int a=10,b=20; //Value of a=10 and b=20

 cout<<"Value of 'a' before Swapping: "<<a<<endl;

 cout<<"Value of 'b' before Swapping: "<<b<<endl;

 a=a+b;     //now a=a(10)+b(20) -> a=30

 b=a-b;     //now b=a(30)-b(20) -> b=10

 a=a-b;     //now a=a(30)-b(10) -> a=20

 cout<<"Value of 'a' after swapping: "<<a<<endl;

 cout<<"Value of 'b' after swapping: "<<b<<endl;

system("pause");

}
Link of Video for more help::
https://youtu.be/9PYADBSffQ0