Since this program will have many include files, you should build your include files like the following example:

-------------------- start of example --------------------
/*

FILENAME: command.h

Here we define a data types for representing a command internally to the program.

*/

#ifndef my_COMMAND_H
#define my_COMMAND_H

#include <string>

enum personType {DOCTOR, PATIENT} ;
enum comCategType {CHECKIN, CHECKOUT} ;
enum priorityType {GREEN, RED} ;

enum specialtyType {PED, GP, INT, CARD, SUR, OBS, PSY, NEUR, ORTH, DERM, OPH, ENT, ERROR} ;

struct commandType
{

bool stop ;
personType person ;
comCategType categ ;
string lastName ;
int age ;
int roomNum ;
specialtyType specialty ;
priorityType priority ;

} ;

#endif
-------------------- end of example --------------------

The directives:

#ifndef my_COMMAND_H
#define my_COMMAND_H

...

#endif

insure that the file will not be included more than once in the image of the program that gets linked together when you call g++. Therefore, you will not get a lot of error messages complaining that things that have been defined already are being redefined.

Note the choice of the "uniquifier" prefix "my_" used to help avoid conflicts with constants that might be defined in system libraries.