swap a and b without tmp var

gistfile1.cpp

#include <iostream>

void swap(int& a, int& b){
  b ^= a; a ^= b; b ^= a;
}

int main(){
  int a = 1, b = 2;
  swap(a, b);

  std::cout << a << " " << b << std::endl;
  
  return 0;