As someone who teaches C to professional engineers, I'd recommend "Hacking: The Art of Exploration" by Jon Erickson. The first 100+ pages are the most succinct coverage of C I've ever come across (if you can already program in other languages).

Also, by following many of the exploits covered in the book, you get a real grasp of what is happening at the machine level - which is one of the major reasons you'd choose C over something more modern.