All you need is K&R, honest.

C is a very simple language. I learned it from K&R in the '80s in an office in a building in a corn field on a back road halfway between Rockford, Il and Belvidire, Il. I went on to hire and assist eight others in acquiring it and then employed them to write, along with myself, a successful machine tool controller of serious sophistication employing a three way tightly coupled Mot 68010 MP system (using bus fault recovery to resolve address collisions) of my design. Not bragging, really, just being dramatic about what you can accomplish starting with just K&R.