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

int round_down(int n, int multiple_of) {
    //int n_rounded_down = (n / multiple_of) * multiple_of;  // CORRECT
    int n_rounded_down = (n * multiple_of) / multiple_of;    // BUG!!!

    // Enforce that the returned value must be an even multiple of 'multiple_of'.
    assert(n_rounded_down % multiple_of == 0);
    // If this is not true, it will deliberately crash our program.

    return n_rounded_down;
}

int main(int argc, char* argv[]) {
    printf("round_down(7, 3) == %d\n", round_down(7, 3)); // → 6
    printf("round_down(8, 3) == %d\n", round_down(8, 3)); // → 6
    return EXIT_SUCCESS;
}
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