EXIT

Purpose

The EXIT statement terminates execution of a DO, Fortran 2008 begins DO CONCURRENT Fortran 2008 ends , or DO WHILE construct before the construct terminates all of its iterations. In addition, it can be used to terminate execution of a specified construct that is not DO, DO CONCURRENT, or DO WHILE.

Syntax

construct_name

The name of a construct.

It can be one of the following constructs:

ASSOCIATE
BLOCK
DO
DO CONCURRENT
DO WHILE
IF
SELECT CASE
SELECT TYPE

Rules

If construct_name is specified, the EXIT statement must be within the construct specified by construct_name. If construct_name is not specified, the EXIT statement must be within the range of at least one DO or DO WHILE construct.

If construct_name is specified, the EXIT statement belongs to the construct specified by construct_name. If construct_name is not specified, the EXIT statement belongs to the DO, Fortran 2008 begins DO CONCURRENT Fortran 2008 ends , or DO WHILE construct that immediately surrounds it.

Fortran 2008 begins An EXIT statement must not be placed within a CRITICAL or DO CONCURRENT construct if it belongs to that construct or an outer construct. Fortran 2008 ends

If an EXIT statement belongs to a DO, Fortran 2008 begins DO CONCURRENT Fortran 2008 ends , or DO WHILE construct, execution of the EXIT statement causes the construct to become inactive. If the EXIT statement is nested in any other DO, DO CONCURRENT, or DO WHILE constructs, they also become inactive. Any DO variable present retains its last defined value. If the DO construct has no construct control, it will iterate infinitely unless it becomes inactive. The EXIT statement can be used to make the construct inactive.

Fortran 2008 begins If an EXIT statement belongs to a construct that is not DO, DO CONCURRENT Fortran 2008 ends , or DO WHILE, execution of the EXIT statement terminates execution of the construct. Any DO, DO CONCURRENT, or DO WHILE loops contained within the construct become inactive.

An EXIT statement can have a statement label; it cannot be used as the labeled statement that terminates a construct.

Examples

Example 1: The following example illustrates the usage of the EXIT statement in the DO and DO WHILE statements:

      LOOP1: DO I = 1, 20
         N = N + 1
10       IF (N > NMAX) EXIT LOOP1           ! EXIT from LOOP1

         LOOP2: DO WHILE (K==1)
            KMAX = KMAX - 1
20          IF (K > KMAX) EXIT              ! EXIT from LOOP2
         END DO LOOP2

         LOOP3:  DO J = 1, 10
             N = N + 1
30           IF (N > NMAX) EXIT LOOP1       ! EXIT from LOOP1
             EXIT LOOP3                     ! EXIT from LOOP3
         END DO LOOP3

      END DO LOOP1

Example 2: The following example shows how the EXIT statement is used to terminate execution of a BLOCK construct:

a : BLOCK
  DO i = 1, num_in_set
    IF (X == a(i)) EXIT a       ! EXIT from the a BLOCK construct
  END DO
  CALL r
END BLOCK a