#include <stdio.h>

    void foo(int i)
    {
        printf("[foo] `i` was %d\n", i);
        i++;
        printf("[foo] Now `i` is %d\n", i);
    }

    int main()
    {
        int i = 0;
        printf("[main] `i` was %d\n", i);
        foo(i);
        printf("[main] Now `i` is %d\n", i);
    }