expressão lógicaLógicoRequired
Condition reevaluated before each iteration. The loop continues only while it returns .T.
COMMANDPublished
WHILE ... ENDDO
WHILE <expressão lógica> ... ENDDORepeats a block of commands while a logical expression remains true.
Overview
WHILE ... ENDDO evaluates its condition before each iteration. If it is true (.T.), the block runs; when it becomes false (.F.), processing continues after ENDDO. EXIT immediately terminates the loop, while LOOP returns to WHILE and reevaluates the condition without executing the remainder of the current block.
Syntax
WHILE <expressão lógica> ... ENDDOParameters
comandosInstruções AdvPLRequired
AdvPL instructions executed on each pass while the condition remains true.
Condition-controlled iteration
User Function ExWhileEven()
Local nNumber := 0
Local nSum := 0
While nNumber <= 100
nSum += nNumber
nNumber += 2
EndDo
MsgInfo("Sum of even numbers: " + CValToChar(nSum))
ReturnExpected result
The condition is checked before each pass. nNumber advances by two until it exceeds 100.
Sequential table reading
User Function ExWhileTabela()
DbSelectArea("SA1")
SA1->(DbGoTop())
While !SA1->(Eof())
ConOut(SA1->A1_COD + " - " + SA1->A1_NOME)
SA1->(DbSkip())
EndDo
ReturnExpected result
The loop processes each record until EOF() indicates the end of the work area. DbSkip() is essential for advancing.
LOOP and EXIT with safe updates
User Function ExWhileControle()
Local nItem := 0
While nItem < 20
nItem++
If nItem % 2 != 0
Loop
EndIf
If nItem > 10
Exit
EndIf
ConOut(CValToChar(nItem))
EndDo
ReturnExpected result
The counter is updated before LOOP. Odd values are skipped and EXIT terminates the loop after the desired limit.
- Use WHILE when the number of iterations depends on a condition that changes during processing.
- Ensure that some instruction in the block can make the condition false.
- Use EXIT to stop early after finding the desired result.
- Use LOOP to skip the rest of an iteration, but update condition-control variables first.
- When reading tables, advance with DbSkip() and combine EOF() with any other required conditions.
- A condition that never becomes false creates an infinite loop.
- LOOP may skip the counter update, DbSkip(), or another instruction required to terminate the loop.
- Every WHILE requires a matching ENDDO; nested structures must be opened and closed correctly.
- Conditions that access fields or functions must remain valid throughout all iterations.
- Very long or deeply nested blocks are harder to test and maintain.