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

typedef struct {
    int x;
    int y;
} Point;

void set_point_to_zero_wrong(Point p) {
    p.x = 0;
    p.y = 0;
    // WRONG because it operates on the copy of the 'Point' object that was passed as an argument.
}

void set_point_to_zero_correct(Point* a_p) {
    a_p -> x = 0;
    a_p -> y = 0;
    // CORRECT because this modifies the object in the caller's stack frame.
}

int main(int argc, char* argv[]) {
    Point p = { .x = 5, .y = 6 };

    printf("BEFORE\n");
    printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);

    set_point_to_zero_wrong(p);
    printf("AFTER set_point_to_zero_wrong(p)\n");
    printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);

    set_point_to_zero_correct(&p);
    printf("AFTER set_point_to_zero_correct(&p)\n");
    printf("p == { .x = %d, .y = %d }\n\n", p.x, p.y);

    return EXIT_SUCCESS;
}
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