gistfile1.c

#include <stdio.h>

void swap(int* a, int* b)
{
    int tmp = *a;
    *a = *b;
    *b = tmp;
}

int main(void)
{
    int a = 10;
    int b = 20;

    swap(&a, &b);

    printf("%d %d\n", a, b);

    return(0);
}