"but I get a compiling error"

WHAT COMPILING ERROR???

Look, at the top of every .h file do this:

#ifndef THE_NAME_OF_THIS_HEADER_FILE
#define THE_NAME_OF_THIS_HEADER_FILE

//Declarations

#endif

DO NOT put all this #ifndef stuff in your .c files before the #include statements, put it in the header files.

Look at the header files supplied with your 'C' compiler or read a 'C' book for goodness sake.