#include <iostream>

auto swap(int x, int y) -> void
{
    auto const tmp = x;
    x = y;
    y = tmp;
}

auto main() -> int
{
    auto i = 1;
    auto j = 2;
    std::cout << i << ' ' << j << '\n'; // prints 1 2
    swap(i, j);
    std::cout << i << ' ' << j << '\n'; // prints 1 2... not swapped?
}