"Any suggestions on what I should apply C to as a way to learn it?" If you are into hardware as well, get microcontrollers and do some home improvement project

"Any suggestions on what I should apply C to as a way to learn it?" If you are into hardware as well, get microcontrollers and do some home improvement projects. The easiest way is to get Raspberry Pi or similar, but if you also want to learn a great deal about system programming, try to bring up MCU on your own, starting with bootloader.