Expert C Programming by Peter van der Linden has some questions you might like to ask in the appendix. Some of them are rather difficult. If you ever read The Art of Computer Programming you will have noted it contains a large number of exercises suitable for this kind of game.

And, please always remember you could meet somebody asking you these questions in an interview.

Christian Lemburg
Brainbench MVP for Perl
http://www.brainbench.com