The most important thing you should know is the way #include works: The #include directive tells the preprocessor to treat the contents of a specified file as if those contents had appeared in the source program at the point where the directive appears. In other words, the compiler replaces all the #include directives by the content of the specified files and builds a single script before compilation. So there is no such a script file rating on the run.

An explanatory example of the #include directive behavior you should never use:
Code:
// main.c
#include <acknex.h>

function main ()
{
   wait(1);
   while ( !key_esc )
   {
      #include "main_loop.c"
   }
   sys_exit ( NULL );
}

Code:
// main_loop.c
draw_text ( "test", 0, 0, COLOR_WHITE );
wait(1);