#include <stdio.h>

void add_one(int q[]) {
    // because 'q' is just a special kind of pointer
    // called a constant pointer, this statement works
    // as you would expect.

    *q = *q + 1;
}

int main() {
    int a = 10;
    add_one(&a);

    // print the updated value.
    printf("%d\n", a);

    return 0;
}