|
WHILE .. WEND |
Repeat Statements |
WHILE expression
...
WEND
|
expression |
An expression whose value determines if the condition is True or False. In numeric expressions, a zero value will indicate FALSE; otherwise, any non-zero value will indicate TRUE. In string expressions, a null (empty or blank) value will indicate FALSE; otherwise, any non-null value will indicate TRUE. |
(The ability to use a string expression was added in PxPlus v10.)
Use the WHILE directive for conditional looping in a program. PxPlus executes all directives between a WHILE directive and the next WEND directive repeatedly until the value of the numeric expression is 0 (zero).
When PxPlus encounters a WHILE directive, it evaluates the numeric expression. If the expression returns a TRUE value (non-zero for numeric, non-null for string), PxPlus continues execution until a corresponding WEND directive is encountered, at which point the numeric expression is re-evaluated. The system continues to loop back to the directive following the WHILE directive until the expression yields a FALSE value. At this point, execution proceeds to the first directive following the WHILE directive's corresponding WEND directive and terminates the loop. Then, control transfers to the statement following the WEND.
If the system encounters a WEND directive but is not currently processing a WHILE/WEND loop, it returns an Error #27: Unexpected or incorrect WEND, RETURN, or NEXT. All FOR/NEXT, GOSUB/RETURN, and WHILE/WEND sequences executed within the WHILE/WEND loop must be completed.
Use a conditional EXITTO or BREAK to exit a WHILE/WEND loop early.
BREAK Immediate Exit of Loop
CONTINUE Initiates Next Iteration of Loop
EXITTO End Loop, Transfer Control
Structured Error Handling Using ON ERR
0100 while A$<>"E"
0110 let K$=key(1,end=1000)
0120 read (1)N$
0130 print "Key: ",K$," Name: ",N$
0140 input "Delete (Y/N):",A$
0150 if A$="Y" then remove (1,key=K$)
0160 wend
0170 stop
1000 print "End-of-file..."
1010 exitto 0170