Open Watcom FORTRAN 77 Language Reference

12 Functions and Subroutines
12.1 Introduction
Functions and subroutines are procedures that fall into one of the following categories.
1. Statement functions
2. Intrinsic functions
3. External functions
4. Subroutines
First let us introduce some terminology.
A program unit is a collection of Open Watcom FORTRAN 77 statements and comments that can be either
a main program or a subprogram.
A main program identifies the program unit where execution is to begin. A main program is a program
unit which has as its first statement a PROGRAM statement or one which does not have a PROGRAM,
FUNCTION, SUBROUTINE or BLOCK DATA statement as its first statement. Complete execution of the
main program implies the complete execution of the program. Each executable program can contain only
one main program.
A subprogram is a program unit that either has a FUNCTION, SUBROUTINE or BLOCK DATA statement
as its first statement. This chapter will only deal with subprograms that have a FUNCTION or
SUBROUTINE statement as its first statement.
12.2 Statement Functions
A statement function is a procedure defined by a single statement. Its definition must follow all
specification statements and precede the first executable statement. The statement defining a statement
function is not an executable statement.
A statement function has the following form.
sf ( [d [,d] ...] ) = e
where:
sf
d
is the name of the statement function.
is a statement function dummy argument.
Statement Functions 243