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(g77-295.info)CYCLE and EXIT

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The `CYCLE' and `EXIT' Statements
---------------------------------

   The `CYCLE' and `EXIT' statements specify that the remaining
statements in the current iteration of a particular active (enclosing)
`DO' loop are to be skipped.

   `CYCLE' specifies that these statements are skipped, but the `END
DO' statement that marks the end of the `DO' loop be executed--that is,
the next iteration, if any, is to be started.  If the statement marking
the end of the `DO' loop is not `END DO'--in other words, if the loop
is not a block `DO'--the `CYCLE' statement does not execute that
statement, but does start the next iteration (if any).

   `EXIT' specifies that the loop specified by the `DO' construct is
terminated.

   The `DO' loop affected by `CYCLE' and `EXIT' is the innermost
enclosing `DO' loop when the following forms are used:

     CYCLE
     EXIT

   Otherwise, the following forms specify the construct name of the
pertinent `DO' loop:

     CYCLE CONSTRUCT-NAME
     EXIT CONSTRUCT-NAME

   `CYCLE' and `EXIT' can be viewed as glorified `GO TO' statements.
However, they cannot be easily thought of as `GO TO' statements in
obscure cases involving FORTRAN 77 loops.  For example:

           DO 10 I = 1, 5
           DO 10 J = 1, 5
              IF (J .EQ. 5) EXIT
           DO 10 K = 1, 5
              IF (K .EQ. 3) CYCLE
     10    PRINT *, 'I=', I, ' J=', J, ' K=', K
     20    CONTINUE

In particular, neither the `EXIT' nor `CYCLE' statements above are
equivalent to a `GO TO' statement to either label `10' or `20'.

   To understand the effect of `CYCLE' and `EXIT' in the above
fragment, it is helpful to first translate it to its equivalent using
only block `DO' loops:

           DO I = 1, 5
              DO J = 1, 5
                 IF (J .EQ. 5) EXIT
                 DO K = 1, 5
                    IF (K .EQ. 3) CYCLE
     10             PRINT *, 'I=', I, ' J=', J, ' K=', K
                 END DO
              END DO
           END DO
     20    CONTINUE

   Adding new labels allows translation of `CYCLE' and `EXIT' to `GO
TO' so they may be more easily understood by programmers accustomed to
FORTRAN coding:

           DO I = 1, 5
              DO J = 1, 5
                 IF (J .EQ. 5) GOTO 18
                 DO K = 1, 5
                    IF (K .EQ. 3) GO TO 12
     10             PRINT *, 'I=', I, ' J=', J, ' K=', K
     12          END DO
              END DO
     18    END DO
     20    CONTINUE

Thus, the `CYCLE' statement in the innermost loop skips over the
`PRINT' statement as it begins the next iteration of the loop, while
the `EXIT' statement in the middle loop ends that loop but *not* the
outermost loop.