Ask HN: Websites with C Programming Questions

Im looking for sites like CodingBat, that offer simple, difficult, really hard problems in C to work on.

Does anyone know of such a site for C Programming only?

I'm trying to learn C coming from a Python/Php/Ruby background.

Thank you!

Write an emulator for an 8-bit Z80 microprocessor and then execute an actual Z80 program.

thanks for the comment, albeit i didnt ask you to give me your idea of a problem, but asked for a site to show problems to solve in C.

reverse a C string in place.