FORTRAN Reference Manual

Introduction to Statements
FORTRAN Reference Manual—528615-001
6-4
Statement Order
Table 6-2 lists the characteristics of each group of statements.
Statement Order
The order of statements in a FORTRAN program can determine whether the program
compiles successfully. The following list describes the order in which you can specify
statements in your FORTRAN program.
•
A PROGRAM statement can appear only as the first statement of a main program.
•
An END statement is required as the last statement of each program unit.
•
The first statement of a subprogram must be a FUNCTION, SUBROUTINE, or
BLOCK DATA statement.
•
Comments can appear anywhere in a program. FORTRAN associates comments
that follow an END statement with the program unit, if any, that begins after the
END statement.
•
Specification statements must precede executable statements, statement function
statements, and DATA statements in a program unit.
•
Within the specification statements, IMPLICIT statements must precede all other
specification statements except PARAMETER statements.
•
Statement function statements must precede all executable statements.
•
If the default type of the symbolic name of a constant is not the correct type, you
must specify the symbolic name’s type prior to its first appearance in a
PARAMETER statement.
•
The PARAMETER statement must precede any statement that refers to the entity
defined by the PARAMETER statement.
•
FORMAT statements can appear anywhere in a program unit.
•
ENTRY statements can appear anywhere in a program unit except in the body of a
block-IF or DO statement.
Table 6-2. FORTRAN Statement Types
Type Action
Program unit Nonexecutable. Marks the beginning or end of a program unit.
Specification Nonexecutable. Specifies the characteristics of the user-defined
symbolic names used in the program.
Assignment Executable. Defines or redefines the values of variables in a program.
Control Executable. Modifies the normal sequential flow of execution in a
program.
I/O Executable. Transfers data between your program and internal or
external files, and returns information about the status of files.