Many of the bugs the quiz wants me to find would be pointed out by my IDE (but I'm not taking the quiz in my IDE...) Also, lots of this code is terrible. Simply adhering to a reasonable style could highlight or eliminate bugs. For example, "variable > other_value - 1"; let's get that "- 1" outta there and use >= instead.

Anyway, although I suggest these would be helped by a modern IDE and some style guides, I'd concede that since this is open source code, it's probably older than modern IDEs...