7. Statements at a glance

This short chapter is a map of the statement set. FORTRAN 77 divides statements into two classes (§7) — executable (they act when the program runs) and nonexecutable (they describe the program to the compiler). Knowing which is which explains the ordering rule from Chapter 3: all the describing comes before the doing.

Nonexecutable statements

These define data, types, and layout. They take effect at compile time; they are never "run."

Statement	Purpose	Chapter
PROGRAM, FUNCTION, SUBROUTINE, BLOCK DATA	program-unit headers	14, 15, 16
IMPLICIT	set default types by initial letter	8
INTEGER, REAL, DOUBLE PRECISION, COMPLEX, LOGICAL, CHARACTER	type declarations	8
DIMENSION	array shapes	8
COMMON	shared storage across units	8
EQUIVALENCE	two names for one storage	8
PARAMETER	named constants	8
EXTERNAL, INTRINSIC	declare procedure names	8
SAVE	retain locals across calls	8
DATA	compile-time initial values	9
FORMAT	I/O layout (referenced by label)	13
ENTRY	extra entry points in a subprogram	15
END	physical end of a program unit	3

Executable statements

These do the work, in flow order.

Group	Statements	Chapter
Assignment	v = e, ASSIGN s TO i	10
Control	GO TO, arithmetic/logical/block IF, DO, CONTINUE, STOP, PAUSE, END	11
Procedure	CALL, RETURN	15
Input/output	READ, WRITE, PRINT, OPEN, CLOSE, INQUIRE, BACKSPACE, ENDFILE, REWIND	12

The order, once more

Within a program unit: header → IMPLICIT → other specifications → statement-function definitions → executable statements → END. FORMAT and ENTRY may appear anywhere; DATA may appear anywhere after the specifications. (Full rule: Chapter 3.)

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forterp notes. The full F77 statement set is implemented. The ordering rule (specifications before executables) is enforced under the F77 dialect; see Chapter 3.