Been a while since you've touched Java or Python? You should check out codingbat.com It has a ton of different methods for you to write for fun, and you're able to test them within the website itself. It's a great resource for you to bring your coding skills back up to speed!
What about CSS, HTML, PHP, and other web development languages? w3schools.com has a similar way for you to be able to brush up on these skills! It also has in depth training tools, and is a worthy knowledge base for any web developer seeking information on how to code very basic actions in web development.
Where's the codingbat for C? Since C is a much more volatile language to code with, they don't have anything like this for C. If they did, the dynamics of the C language are so diverse, that you would be able to manipulate the website with easy injection. Websites would crumble from anyone with experience who is intentionally trying to destroy the site.
If you'd like to brush up on your C, there are plenty of other free materials on the web, like cprogramming.com for you to be able to hone your skills. In order for you to test to see if your code is working in C, you would have to code locally, on your own PC -- not over the internet.