Recommended and mentioned products
A free source code editor which supports several programming languages running under the MS Windows environment.
But I'm going to plead for sanity and say do NOT use vanilla Windows notepad. The crappiness of the undo/redo and the lack of line numbering will make your life unnecessarily painful. For something minimal but still remotely usable, I'd personally recommend Notepad++.
C, C++, Objective C and Objective C++ front-end for the LLVM compiler.
In addition to the answers already here, there's also Clang which is known for friendly error messages and additional memory safety features.