Hm, I wonder what kind of questions that entailed. Because unsigned arithmetic in C seems very intuitive to me. I have a hard time coming up with a question that would be hard to answer. Certainly, if we're talking about the C standard, unsigned integers are much more intuitive than signed integers.

Although even if there somehow are hard questions, I'm not sure understanding unsigned arithmetic would have helped whoever wrote that code. Because I think if you asked that person "what does this unsigned type do with -5 C?" the answer would have been pretty obvious.