I read K&R 20 years ago and today it's still the closest programming book to my heart -- yeah there's more modern choices but the exercises are unmatched, it's short, and it's one of the most fun books you'll ever read.

The standards for C99, C11 are open. Look up what you don't learn in them and grab one of the other more modern suggestions from here for that, but K&R is a must have for any C programmer.

You probably won't be able to put the book down if you start reading it.