#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
#define print_int_expr_and_value(n)  printf("%s == %d\n", (#n), (n))

int round_to_nearest_multiple_of_10(int n) {
    int result; // not initializing because it will be initialized in the if or the else clause (↓).
    if(n % 10 <= 4) {
        result = (n / 10) * 10;
    }
    else {
        result = (n / 10) * 10 + 1;  // BUG (planted)
    }
    assert(result % 10 == 0);   // no matter what:  result must be a multiple of 10.
    return result;
}

int main(int argc, char* argv[]) {
    print_int_expr_and_value( round_to_nearest_multiple_of_10(14) );
    print_int_expr_and_value( round_to_nearest_multiple_of_10(18) );
    
    return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */