C Traps and Pitfalls (1988) [pdf]

The book of the same name is a decent third book on C: K&R or some other intro, Expert C Programming, then this.

"Incidentally, it is a common misconception that if c is a character variable, one can obtain the unsigned integer equivalent of c by writing (unsigned) c. This fails because a char quantity is converted to int before any operator is applied to it, even a cast. Thus c is converted first to a signed integer and then to an unsigned integer, with possibly unexpected results."

The "even a cast" part is wrong. The usual arithmetic conversions (including the integer promotion) is not done with the cast operation in C.

Lots of code in there is deprecated. Don't use it.