HP Fortran Programmer's Reference (September 2007)

Language elements
Program structure
Chapter 244
Program structure
A complete executable Fortran program contains one and only one main program unit and
may also contain one or more of the following other types of program units:
• External function subprogram unit
• External subroutine subprogram unit
• Block data program unit
• Module program unit
Each program unit can be compiled separately. Execution of the program starts in the main
program. Control may be passed to other program units.
The Fortran 90 program units, and the transfer of control between them, are described in
Chapter 7, “Program units and procedures,” on page 153.