#include <stdio.h>
#include <stdlib.h>

void swap (int *a, int *b);

int main (int argc, char *argv[]) {
        if (argc != 3) {
                printf("usage: %s (int x) (int y)\n", argv[0]);
                return EXIT_FAILURE;
        }

        int x, y;

        x = (int) argv[1];
        y = (int) argv[2];

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

        swap(&x, &y);

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

void swap (int *a, int *b) {
        int temp;

        temp = *a;

        *a = *b;
        *b = temp;
}