#include <stdio.h>

void swap(int *x, int *y)
{
    int t = *x;
    *x = *y;
    *y = t;
}

int main(void)
{
    int x, y;

    x = 10;
    y = 20;

    swap(&x, &y);

    printf("x = %d, y = %d\n", x, y);

    return 0;
}