C has no concept of classes, so a literal translation of that (seriously poor already) code would take major effort to add a "class-like" implementation in C. This is not going to happen.
Even if it did, the resulting code would be very, very poor quality C code - there are better ways to handle the data in C that trying to reinvent classes because that's the code you found and hope will answer you homework assignment. It probably won't, not without lots of mods, and the code quality won't get you a grade anyway.
And ... two other things:
1) We aren't a code conversion service. You want that, you go pay for it at freelancer.com
2) We are more than willing to help those that are stuck: but that doesn't mean that we are here to do it all for you! We can't do all the work, you are either getting paid for this, or it's part of your grades and it wouldn't be at all fair for us to do it all for you.
So we need you to do the work, and we will help you when you get stuck. That doesn't mean we will give you a step by step solution you can hand in!
Start by explaining where you are at the moment, and what the next step in the process is. Then tell us what you have tried to get that next step working, and what happened when you did.
Just finding code on the internet and hoping you can hand it is isn't going to work at all...
If you are having problems getting started at all, then this may help: How to Write Code to Solve a Problem, A Beginner's Guide