C++ Problem (9) : How to swap two numbers without using third variable?

 C++  (9) : How to swap two numbers without using third variable?

#include<iostream>

using namespace std;

int main(){

double a,b;

cout<<"*****Swapping two numbers without using third variable.*****"<<endl;

cout<<"Enter first number."<<endl;

cin>>a;

cout<<"Enter second number."<<endl;

cin>>b;

cout<<"Before swapping:"<<endl;

        cout<<"a = "<<a<<endl;

        cout<<"b = "<<b<<endl;

       a=a+b;

       b=a-b;

       a=a-b;

cout<<"After swapping:"<<endl;

        cout<<"a = "<<a<<endl;

        cout<<"b = "<<b<<endl;

return 0;

}

Output:

*****Swapping two numbers without using third variable.*****

Enter first number.

10

Enter second number.

5

Before swapping:

a = 10

b = 5

After swapping:

a = 5

b = 10