using your C code and a serial port to send receive data from the PIC, its like communicating with 2 computers via null modem cable in the old days. I use VB.net and its got a prebuilt in control for serial communication, if your using visual c/c++ it should have that too. to communicate with PIC USB Ports you should have to use a HID.dll file to communicate I think. Not sure how to do this on C, but in microcode studio it has a HID maker.

But I would try just interfacing with the PIC via serial port to get the understanding and your program in c working first then change the type of communication.