I took a class of programming at my university and I am working on some program. I want to know if it is possible to program my own kbhit() function. And if it is possible to look, how kbhit() is coded.
The purpose is that I need to know how functions I use work.
Yes and no.
C language has no notion of input and output. It relies on a standard library (essentially written in C) that in turn relies on system calls.
Neither the standard library, nor the set of system calls common to Unix-like systems and Windows deal with non blocking system calls, so you have to call system specific ones.
But again, you can call them easily from C language.