This code serves as the boilerplate code that everyone in the MINOR league is allowed to copy. Although you could probably do this hackathon without ever taking a look at most of the code. I would advise you to go through it as it contains many tips to improve your bot.
The eval function is in src/evaluate.c, it very primitive. You should probably
improve that :)
Also the searching currently is limited to depth 4 in src/search.h, while this
probably will work in the tournament (no guarantees). You probably will want to
somehow keep track of the time spent searching.
For people in the major league, you are allowed to copy only and absolutely only the code for handling UCI and FENs. See src/uci.c and src/position.c.