Function            to24hour - converts hours to 24-hour format

  Syntax              #include <timehk.h>
                      (int) to24hour(hr)

  Prototype in        timehk.h

  Remarks             converts midnight (0) to the 24th hour.

  Return value        returns 0 if hr is midnight (0), otherwise returns
                      hr.

  See also            isPM(), time_convert(), tohour()