divmod needs to hand back two results from one call – a quotient and a remainder – and a C function can only
return one value. Complete it using the two pointer out-parameters quotient and remainder: write each result
through its pointer rather than returning anything.
The arithmetic itself is just / and %; the exercise is entirely about the out-parameter mechanics. Note the
last sample case: since C99, / truncates toward zero and % follows it, so -17 / 5 is -3 (not -4) and
-17 % 5 is -2 (not 3) – this is guaranteed by the standard, not a compiler quirk, so you can rely on a / b
and a % b giving you these exact values without any special-casing.