Are you looking to exercise your algorithms or your syntax? Usually beginner-level exercises like you've requested work on one or the other
I'd suggest just getting a book from the library/googling - it's how I learned. They usually have pretty good examples and exercises, and they're also handy for reference.
I also took a computing competition when I was in high school - check it out here:
http://contest-cemc.uwaterloo.ca/ccc/index.html
They have many problems similar to the one Quadraton just posted. If I remember the contest correctly, the Junior-level problems would be about your skill level. You might need to learn file i/o, but that's fairly simple if you're already accustomed to screen i/o
C: fopen(), fclose(), fprintf()
C++: fstream open, close, <<, >>