For the language, K&R is good, and Expert C Programming: Deep C Secrets by Peter van der Linden is a great second book. But all the fun stuff happens when you

For the language, K&R is good, and Expert C Programming: Deep C Secrets by Peter van der Linden is a great second book. But all the fun stuff happens when you start talking with your OS, so get a book about that too. If you are planning to develop on Linux, Michael Kerrisk's The Linux Programming Interface is excellent. Much of it will be familiar to someone used to shells and the terminal, but there will be plenty of new ideas too, and even the stuff you know will get a much deeper perspective.