C++ exercises: swap two variables

Q: Swap a and b without using a third variable.

Algorithm:
1. a(new) = a(old) + b(old);
2. b(new) = a(new) - b(old) = (a(old) + b(old)) - b(old) = a(old)
3. a(final) = a(new) - b(new) = (a(old) + b(old)) - a(old) = b(old)

#include <iostream>

using namespace std;

int main()
{
   int a = 123;
   int b = 200;

   cout << "a: " << a << ", b: " << b << endl;

   a = a + b;
   cout << "a: " << a << ", b: " << b << endl;

   b = a - b;
   cout << "a: " << a << ", b: " << b << endl;

   a = a - b;
   cout << "a: " << a << ", b: " << b << endl;

   return 0;
}