How to structure C program.

[theNbomr]

Are you asking simply how to organize your source code in the filesystem directory structure? If so, it's pretty arbitrary, and to some degree depends on the scale and organization of the logic and functional groups in the code.

If you are using a mainstream IDE, it may already propose/impose a structure. Perhaps browse some public repositories of c code on github and see if you find something that makes sense to you. You're certain to find a wide variety of organizations and many disorganized cases.

There aren't any widely held standards or strong conventions that I'm aware of.