Why does this program swap the values?

Question

I have the following code:

#include "stdafx.h"
#include <iostream>
using namespace std;
#include <conio.h>
#include <cstring>
#include <iomanip>

void swap(long a, long b)
{
    long temp;

    temp=a;
    a=b;
    b=temp;
}
int _tmain(int argc, _TCHAR* argv[])
{
    int x = 5, y = 3;
    cout << x ;
    cout << y << endl;

    swap(x, y);

    cout << x ;
    cout << y << endl;

    getch();
    return 0;
}

The program gives the output:

5 3

3 5

The program actually swaps the values! Why is that? The parameters of the swap() are not pointers or references.

(I am using VS 2005)