need help swaping integers

[ryanpeppers]

#include <iostream>
#include <stdlib.h>

using namespace std;

void swap_integers(int x, int y);

int main()
{
    int num1 = 15;
    int num2 = 16;
    cout << num1 << " " << num2 << endl;
    swap_integers(num1,num2);
    cout << num1 << " " << num2 << endl;
    system("Pause");
    return 0;
}

void swap_integers(int x, int y)
{
    int atemp = x;
    x = y;
    y = atemp;
}

i get

15 16
15 16
Press any key to continue . . .

should be

15 16
16 15
Press any key to continue . . .

what am i doing wrong?

[quirkyusername]

you're passing x and y into the swap function by value, which means a copy is made of them and those copies are the only things which are swapped, not the original values.

Pass them in by reference to solve this.

[moorecm]

And if you don't have to implement your own, try std::swap.

[ascii]

The most efficient way to swap two variables is with the XOR method :)

x ^= y;
y ^= x;
x ^= y;

[Disch]

The most efficient way to swap two variables is with the XOR method :)

[citation needed]

That method only works with integers, and involves 3 operations.

The more traditional approach:

T temp = x;
x = y;
y = temp;

works with any copyable type T and also only involves 3 operations.

Note that std::swap effectively does exactly that.

I suppose the temp method is "less efficient" in that it needs an additional register for the temporary. But come on.

[ascii]

Hehe I suppose that's true. It doesn't even matter as this is a rather trivial task. The only time I can think of where swapping variables would be necessary is when sorting an array, and there are plenty of library functions for that.

[Ashishduh]

Well actually, the temp variable swapping is more efficient because you need to make sure x != y or XOR wont work, so that's an added statement :)

[bl4ckb3rry]

You should pass x and y by reference:

void swap_integers(int &x, int &y)
{
      int atemp = x;
      x = y;
      y = atemp;
}

And btw, avoid using system functions - such as system("Pause").