gets() is used a lot in ancien learning material for C. That said, it is unsafe and therefore removed in recent C versions. A simple #define can bring it back rather securely.

This is the line you need to add to your C files.

#define gets(x) fgets(x, sizeof(x), stdin)

Don’t add it in a header file, only in each C file.

The sizeof will only be correct in the case of statically defined buffers.

If it is a dynamic buffer, it is still secure, but incorrect. With a simple pointer, the sizeof will only be the of the size of a single element.