pTAL Reference Manual (H06.08+)

Statements
HP pTAL Reference Manual—523746-006
12-18
DO-UNTIL
condition
is either:
•
A conditional expression
•
An INT, INT(32), or FIXED arithmetic expression. If the result of the arithmetic
expression is not 0, condition is true. If the result is 0, condition is false.
If condition is false, the DO-UNTIL statement continues to execute. If
condition is true, the statement following the DO-UNTIL statement executes.
A DO-UNTIL statement always executes at least once (unlike the WHILE on
page 12-45).
In Example 12-14 on page 12-18, the DO-UNTIL statement loops through array_a,
testing the content of each element until an alphabetic character occurs.
In Example 12-15 on page 12-18, the DO-UNTIL statement loops through array_a,
assigning a 0 to each element until all the elements contain a 0.
The conditional expression cannot reference hardware indicators (<, <=, =, <>, >, >=,
'<', '<=', '=', '<>', '>', '>=', $OVERFLOW, and $CARRY). Only IF statements can test
hardware indicators. For more information, see Section 13, Hardware Indicators.
To use a hardware indicator’s value to control a DO-UNTIL loop, save the hardware
indicator’s value and either test the saved value (as in Example 12-16 on page 12-19)
or execute an explicit GOTO statement to exit the loop (as in Example 12-17 on
page 12-19). Hardware indicators cannot appear in the conditional expression of a DO-
UNTIL statement.
Example 12-14. DO-UNTIL Statement
index := -1;
DO index := index + 1 UNTIL $ALPHA (array_a[index]);
Example 12-15. DO-UNTIL Statement
LITERAL limit = 9;
INT index := 0;
STRING .array_a[0:limit];y
DO
BEGIN ! Compound statement to execute in
array_a[index] := 0; ! DO loop
index := index + 1;
END
UNTIL index > limit; ! Condition for ending loop