HP 3000 Manuals HP 3000 Manuals
Chapter 5 Subprograms
A subprogram is an independent section of code called by a main program
or by another subprogram. Subprograms make programs more readable and
easier to maintain, write, and debug.
Subprograms can be grouped into these three categories:
* Subroutines
* Functions
* Function subprograms
* Statement functions
* Intrinsic functions
* Block Data Subprograms
A program unit, such as a main program or a subprogram, is a sequence of
FORTRAN statements. Table 5-1 summarizes the components of program
units.
Table 5-1. Components of Program Units
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| | | |
| Component | Description | How Identified |
| | | |
----------------------------------------------------------------------------
| | | |
| Main program | Defines the main entry | Can begin with the PROGRAM |
| | point. | statement. |
| | | |
----------------------------------------------------------------------------
| | | |
| Subroutine | Returns values through | Begins with the SUBROUTINE |
| | argument lists or common | statement. |
| | blocks. | |
| | | |
----------------------------------------------------------------------------
| | | |
| Function | Returns values through the | Begins with the FUNCTION |
| | function name, argument | statement. |
| | lists, or common blocks. | |
| | | |
----------------------------------------------------------------------------
| | | |
| Statement | Calculates a single | Defined in a program unit. |
| function | result; cannot be | |
| | referenced outside of the | |
| | program unit that defines | |
| | it. | |
| | | |
----------------------------------------------------------------------------
| | | |
| Block data | Provides initial values | Begins with the BLOCK DATA |
| subprogram | for named and blank common | statement. |
| | blocks. | |
| | | |
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This chapter describes subroutine, function, and block data subprogams.