Sean recently posted a link to a C tutorial, and this chapter is on graphics in C.
The specific library they work with is SDL and is designed for use with Pelles C, which is free, and has a full IDE, and lots of other features, included with it, including a forum.
The latest version of Pelles C is C99 compliant, even
I'm looking for opinions on Pelles C (which I've never heard of before).
I don't change software readily, but this looks quite inviting.
Info and screen shots, etc., are here: