A lot of these aren't C or C++ specific. Many of them were typos, for example.

There are also some ambiguities. At least two questions I encountered contained more than one bug, or at least one explicit bug and one "occasional" bug due to a lack of testing in the code (say, for division by zero).

Also, it'd be a a good idea to put a disclaimer for the quiz taker to assume types, variables and other tokens are declared properly. It's easy to make the deduction after getting the first question which you get incorrect because you chose the "wrong" bug.