If you want something simpler for new students
our 2014 robot code is very minimalist (no feedback loops or fancy objects) while still containing most of what you'd find in typical FRC code.
We typically have a generic skid-steer drivebase on hand for new programmers to work with after giving them a crash course on the control system and introducing them to C syntax and OOP (we start out by teaching them about variables, loops, scope etc. then give them challenges they must complete on their own like sorting an arbitrary array). When they're competent at programming we teach them WPI lib, and when they can make a simple robot run we have them start deriving drivebase kinematics and learning control loops on their own with a little bit of guidance and oversight. We also have 0 programming mentors on our team, so this is all done by student captains.
Our robot code this year was written entirely by sophomores on the team who were completely new to programming last year and has had PID-corrected strafe, field centric and robot centric holonomic drive code (from when our robot had slide drjve lol), a position and velocity PI controller for our elevator and more all designed by them.