For the last recruit tests I gave, it was the easiest way to discard applicants without proper C knowledge. A wrong answer predicted a bad score on pratical (and lenghty) tests like code commenting, finding bugs, etc.

Anecdote: When corrected, a guy who allegedly coded in C for 10 years even asked what was the use for main to return something :-(( So we talked about unix return values, $? in bash and he had a spark in his eye. I had a tear in mine.