The following offer guidance relating to common issues. If you don't find your problem listed here, you should check the lab issues wiki. You may also want to investigate some common mistakes in C.
If you want to work on the exercises away from the practical sessions, you can install the Web Edition of the Quartus tools which needs no license setup beyond registration and works outside the Cam domain. Take care when mixing the Web edition with the Subscription edition as the .sof output files (that you program onto the FPGA) have different names (see 'OpenCore Plus Status' below). Make sure you aren't programming an old version of your design.
If you need to use the full Subscription version of the tools, access to the license server for the Subscription version is available from the cam.ac.uk domain - email theo.markettos at cl.cam.ac.uk for details.