Not in any particular order:
1) There is some funky html there that ought to be styled via css IMO (your header nav list for example).
And while not always perfect, the W3C validation tool does come in handy at times to make sure there are no "obvious" mistakes.
2) Also, you have the w3c certified image on the page, but it doesn't link to YOUR certification, which is the point of having it on the site (not sure if this was intentional or not). This may not be a design issue, but more of a customer issue.
Overall, I like the purpose of the site, but there are some issues that I would expect a "teacher" to have resolved so that trust can be established. It is almost like doing to an auto mechanic who always has a broken down car....doesn't instill a lot of confidence from the customer's perspective.
However, I guess this depends what your target audience is. Most people may not be as picky as designers so these issues may be overlooked.
So just from a customer perspective (and not technical or design), the purpose is interesting. I'm not a fan of the color scheme (too girly for me I guess).
3) I just noticed a weird error: http://cprogramming.host22.com/Pages/Characters/char4.html
The navigation menu appears in an iframe at the bottom of that example page. Looks like it occurs at the bottom of every example's page. That's a deal breaker for both designer and customer probably.
4) Also, the "Wishlist" thing that says to post your favorite video, song, text, etc... seems out of place. 1) what is it for? 2) How is it related to learning C? 3) How is someone supposed to post that stuff?
5) If you are going to post code as examples, you may want to take a look at this article describing "best practices": http://www.sitepoint.com/best-practice-for-code-examples/
There seems to be some both design decision issues as well as technical issues. As a result, I can't rate it because from my perspective, it isn't finished yet. I commend the idea and encourage you to keep going with it, but I also think you need to work on the design as it isn't finished.