Parameters passing - Call by reference

#include <iostream>
#include <string>
using namespace std;

void swap(int &x, int &y)
{
    int temp = x;
    x = y;
    y = temp;
}
int main()
{
  int a = 10;
  int b = 40;

  swap(a, b);
  cout << a << " " << b << endl;
}