FORTRAN Reference Manual

Program Units
FORTRAN Reference Manual—528615-001
4-8
Subroutines With Alternate Return Specifiers
When a CALL statement executes, FORTRAN first evaluates any actual arguments
that are expressions, and then associates the actual arguments with the dummy
arguments specified in the SUBROUTINE statement. The CALL statement then
transfers control to the subroutine.
The subroutine subprogram must contain the following statements:
•
A SUBROUTINE statement as its first statement
•
An END statement as its last statement
In addition to these two statements, you can use any FORTRAN statement in a
subroutine except PROGRAM, FUNCTION, BLOCK DATA, or another SUBROUTINE
statement. Write the SUBROUTINE statement in the following form:
SUBROUTINE name ( dummy-argument-list)
As Example 4-1 on page 4-7 shows, a SUBROUTINE statement does not require a
dummy argument list or the parentheses that would enclose a dummy argument list.
Subroutines With Alternate Return Specifiers
Normally, when a subroutine executes, it returns control to the statement following the
CALL statement. However, you can specify an alternate point of return from a
subroutine by including an actual argument in the following form in the actual argument
list in the calling statement:
* label
label is the label of a statement in the calling program unit to which the called
subroutine can return.