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

// 55, m=10, 50
// 57, m=5   55
int _round_down(int n, int multiple_of) {
    assert(multiple_of != 0);
    int n_rounded_down = (n / multiple_of) * multiple_of;
    return n_rounded_down;
}

int main(int argc, char* argv[]) {
    printf("55 rounded down to the nearest 10 is %d\n", _round_down(55, 10));
    printf("57 rounded down to the nearest  5 is %d\n", _round_down(57,  5));
    printf("57 rounded down to the nearest  0 is %d\n", _round_down(57,  0));
    return EXIT_SUCCESS;
}
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