I'm currently brushing up on C programming and I'm looking for an online site that teaches the language through a series of programming problems.
These problems would gradually increase in complexity and focus on introducing one or two new concepts of the language as the user/student learns more.
I'm familiar with the UVa Online Judge site, and Project Euler. Both of these sites are great for practicing coding in general, but I'm looking for something similar which is focused on teaching a language.