Apple - Is there a C compiler for iPad?

A cursory look at the iTunes Store reveals CodeToGo (iTunes Store Link). Since you cannot compile on the iPad itself, this app leverages a web service (IDEOne) in order to run the program and return the results to your device. The app is USD$3 and a universal binary (iPhone+iPad). The web service appears to be free, if not just a little ugly :).

If you have an internet connection, you could use codepad.org. They let you compile many different languages from code you paste into a web form. Supports a lot of formats and has some nice sharing features.

If you're willing to jailbreak, the answer is yes. You can install GCC (the same open-source C compiler included with XCode) on your iPad.

The process is a bit complicated, but it's certainly possible. You can find instructions here. The instructions I've linked only mention the iPhone, but the same process should work on the iPad.

If you're not willing to jailbreak, then the solution VxJasonxV suggested might be your only option.