To be picky, the general rule is that q goes before u only if u is followed by another vowel (qui, quo, qua), c is used in the other cases, but - of course - th

To be picky, the general rule is that q goes before u only if u is followed by another vowel (qui, quo, qua), c is used in the other cases, but - of course - there are a few exceptions, the most common being "cui".