``p480.h''

Sometimes header files (like ``p480.h'') end up included twice, once in the main program and once in another header file, which can cause difficulties at compile time. A standard trick to avoid this is to have the header define a variable for the C preprocessor and also to check whether it is defined. To do this simply add the following two lines to the very top of your ``p480.h'' file,

#ifndef _P480_H_
#define _P480_H_

and the following line to the very bottom,

#endif

Each ``.h'' file which you make should have its own distinct marker variable like this to avoid multiple inclusions.