Open Watcom FORTRAN 77 Language Reference

Program Structure Control Statements
Example:
LOOP
WRITE( UNIT=*, FMT=’(A)’ ) ’Enter a number’
READ( UNIT=*, FMT=’(F10.4)’, IOSTAT=IOS ) X
IF( IOS .NE. 0 ) CYCLE
IF( X .LT. 0 ) EXIT
PRINT *, X, SQRT( X )
END LOOP
The above statements read and print values until a negative integer value is entered. If an input error
occurs, the input operation (READ) is retried using the CYCLE statement. The CYCLE statement causes
control to resume at the END LOOP statement which then immediately transfers control to the statement
following the LOOP statement.
Example:
CHARACTER RECORD(80)
LOOP : RDREC
READ(5,100) RECORD
AT END, STOP
DO I = 1, 80
IF( RECORD(I) .LT. ’0’
+ .OR. RECORD(I) .GT. ’9’ )THEN
PRINT *, ’INVALID RECORD’
CYCLE : RDREC
ENDIF
END DO
WRITE(6,101) RECORD
END LOOP
The above example reads in records and verifies that they contain only numeric data. If the record does
not, the input operation is tried again. The CYCLE statement is within three levels of nesting: the IF, the
DO-loop, and the LOOP-END LOOP structure. If a non-numeric character is found, the CYCLE :
RDREC statement will cause control to be passed to the READ statement that follows the LOOP statement.
9.16 AT END
(READ statement)
AT END DO [: block-label ]
statement(s)
END AT END
or
(READ statement)
AT END, statement
The AT END control statement, an extension to FORTRAN 77, is an extension of the END= option of the
FORTRAN READ statement for sequential files. It allows a statement or a block of code following the
AT END 211