I actually don't know any C programs, but that's next on my list. I really am trying to get more into SQL, because it's a really powerful database when combined with other languages. I did some PHP, but I got about halfway through it and it was pretty boring to me.
EDIT: Get back into learning Java! It's amazing! I use it for my AP Computer Science class, and I've learned so much. It's an extremely strong language, and in all honesty, though it's a bit clunky, it is one of my favorites.
Edit 2: I forgot to mention ReactJS as well.