Open Watcom FORTRAN 77 Language Reference

Program Structure Control Statements
Example:
LOOP
READ *, X
IF( X .EQ. 99.0 )EXIT
PRINT *, X
END LOOP
The above statements cause values to be read and printed, one to a line, until the value 99.0 is read. When
variable X has this value, the logical expression in the IF statement evaluates as true and the EXIT
statement causes a transfer of control to the statement following the END LOOP statement. The EXIT
statement is discussed in more detail in a later section.
9.7 WHILE - END WHILE
WHILE( logical-expression )DO
statement(s)
END WHILE
[: block-label]
This extension to FORTRAN 77 causes its block of code to be executed repeatedly while the parenthesized
logical expression is true. The logical expression is evaluated before entry to the block. If the value is
false, control passes to the statement following the END WHILE statement. If the logical expression is
true, the statements of the block are executed. When the END WHILE statement is reached, the WHILE
logical expression is re-evaluated and the above program control decisions are repeated. An optional block
label may be specified (see the CYCLE, EXIT or QUIT statement for more information). An example
follows:
Example:
WHILE( J .GT. 0 )DO
A(J) = B(I + J)
J = J - 1
END WHILE
If variable J is zero or negative when the WHILE statement is executed, the WHILE block of code will be
by-passed and the statement following the END WHILE statement will be executed.
If variable J is greater than zero when the WHILE statement is executed, the WHILE block will be executed
repeatedly until J becomes equal to zero. The effect of this loop will be to assign values to elements of
array A from array B, starting with the element of A corresponding to the initial value of variable J and
working backwards down the array to element 1.
9.8 WHILE - Executable-statement
WHILE( logical-expression )stmt
WHILE - Executable-statement 199