czardas

When a Loop isn't a Loop

28 posts in this topic

#1 ·  Posted (edited)

In the following scenario I wish to run a sequence of tests until a satisfactory condition is met. Then the remaining tests are skipped.

;

Local $bCondition = False

Do
    ; test 1
    If $bCondition Then ExitLoop

    ; test 2
    If $bCondition Then ExitLoop

    ; Debug or get out of the script.

Until True ; Loop will not repeat.

; continue...

;

I could do the same thing in other ways but this is nice and clear: keeping everything in one place has certain merits. The problem I have is trying to convince myself that using a loop which never repeats (Do...Until True) actually qualifies as good programming. I keep asking myself why use a loop at all when it isn't really needed?

Do you think I should do this differently, or should I leave it the way it is? :think:

Edited by czardas

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#2 ·  Posted (edited)

The condition "true" will be met in just one pass I suppose. (and no need to repeat the test to check again if some condition has changed)
so if the true condittion will not be met, you will be catch in an endless loop or you need an one further check at the end

maybe you could use a (For ...  next) loop instead of (Do...Until True) to avoid the last check.... ?
 

For $i = 1 To 1 ; only one pass anyway

    ; test 1
    If $bCondition Then ExitLoop

    ; test 2
    If $bCondition Then ExitLoop

Next

; continue...

edit:

corrected 0 to 1 with 1 to 1

Edited by Chimp

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If the loop is never repeated it is useless (IMHO).

Why not simply remove it and add some comment lines to reach your goal: "nice and clear: keeping everything in one place"

; --------------
; Test code starts here
; --------------
Local $bCondition = False
; test 1
If Not $bCondition Then Test1()
; test 2
If Not $bCondition Then Test2()
; --------------
; End of Tests 
; --------------

; continue.

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Chimp - Your loop For ($i = 0 To 1) will run twice. I modelled the approach on the expression While 1: being equivalent to While True. It appears to work in the same way.

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#5 ·  Posted (edited)

 

If the loop is never repeated it is useless (IMHO).

Why not simply remove it and add some comment lines to reach your goal: "nice and clear: keeping everything in one place"

; --------------
; Test code starts here
; --------------
Local $bCondition = False
; test 1
If Not $bCondition Then Test1()
; test 2
If Not $bCondition Then Test2()
; --------------
; End of Tests 
; --------------

; continue.

 

Having to keep testing conditions will impact performance. The idea is to skip all subsequent tests and conditions.

Edited by czardas

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#6 ·  Posted (edited)

Chimp - Your loop For ($i = 0 To 1) will run twice. I modelled the approach on the expression While 1: being equivalent to While True. It appears to work in the same way.

 

.... I was editing my post while you was typing.....

anyway, (for next) should avoid possible endless loops....

Edited by Chimp

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How many tests do you run? In your OP you are testing the condition as well. Maybe not as often as in my code but such a test doesn't increase runtime dramatically.


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Hmm, conditions are sometimes inside other loops. Here's a snapshot.

;

Do
    ; First attempt to divide by factors of 10
    While StringRight($aSciNotation[$iLo][0], 1) = "0"
        $aSciNotation[$iLo][0] = Execute(StringTrimRight($aSciNotation[$iLo][0], 1))
        $aSciNotation[$iHi][1] -= 1
        If $aSciNotation[$iHi][1] = 0 Then ExitLoop 2 ; no need to go any further
    WEnd

    ; More loops and conditions.

Until True

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Then I would stick with your current approach.

Seems to be the best way to do what you want.

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#10 ·  Posted (edited)

Thanks water.

I suppose the more standard approach would be to remove this part of the code to a different function and return according to whatever condition. I could still do that, but I think it might make it harder to follow the flow of arguments. Keeping everything in one place also avoids having to pass a number of parameters to a different function. I asked because I was wondering what opinions people might have.

Edited by czardas

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When I start a new project my code should be as clean as possible (means: adhere to good coding practices. A good starting point is the "Good Coding Practices" thread on the forum).

Over time the code gets more complex as new functionality gets implemented.  The script should be so well documented that you still understand what you have intented with your code even when you have a look at it again a few years later.

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Is it not feasible to just use Else and Return?


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#13 ·  Posted (edited)

You might consider recursion.

_Test ()

Func _Test()
    ConsoleWrite("Test condition" & @LF)
    ;if test is not zero
    If Random(0, 10, 1) Then
        Sleep(10)
        _Test()
    EndIf
    _Continue()
EndFunc

Func _Continue()
    ConsoleWrite("Condition met" & @LF)
    Exit
EndFunc

EDIT:

I don't know if this is pertinent or just stupid, but you could also unwind the recursion, but that ironically requires a loop  :rolleyes:

_Test ()

Func _Test()
    ConsoleWrite("Test condition" & @LF)
    Local Static $Unwind = 0
    ;if test is not zero
    If Random(0, 10, 1) Then
        $Unwind += 1
        Sleep(10)
        _Test()
    EndIf
    While $Unwind
        ConsoleWrite("Unwind" & @LF)
        $Unwind -= 1
        Return
    WEnd
    _Continue()
EndFunc

Func _Continue()
    ConsoleWrite("Condition met" & @LF)
    Exit
EndFunc
Edited by JohnOne

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#14 ·  Posted (edited)

Is it not feasible to just use Else and Return?

 

Using Return would exit the function, and not the contained region.

You might consider recursion.

 

Nope! I don't see how that is useful here. It's unfinished code, but here's a bit more of it. I am using ExitLoop() to skip forward however many steps (notice the aborted attempt).

;

Do
        ; Some preprocessing goes here

        If StringLen($aSciNotation[$iHi][0]) + $aSciNotation[$iHi][1] <= 15 Then ExitLoop ; no need to go any further

        ; First attempt to divide by factors of 10
        While StringRight($aSciNotation[$iLo][0], 1) = "0"
            $aSciNotation[$iLo][0] = Execute(StringTrimRight($aSciNotation[$iLo][0], 1))
            $aSciNotation[$iHi][1] -= 1
            If $aSciNotation[$iHi][1] = 0 Then ExitLoop 2 ; no need to go any further
        WEnd

        ; Attempt division by factors of 5, followed by factors of 2.
        Local $iExpansion, $aFactor[2] = [5, 2]
        For $i = 0 To 1
            While Mod($aSciNotation[$iLo][0], $aFactor[$i]) = 0 ; Integer division is possible.
                $iExpansion = Int($aSciNotation[$iHi][0] * $aFactor[1 - $i])
                If $iExpansion >= 1.0e+15 Then ExitLoop ; Abort the current attempt.

                $aSciNotation[$iHi][0] = $iExpansion
                $aSciNotation[$iLo][0] = Int($aSciNotation[$iLo][0] / $aFactor[$i])
                $aSciNotation[$iHi][1] -= 1
                If $aSciNotation[$iHi][1] = 0 Then ExitLoop 3 ; no need to go any further
            WEnd
        Next

        ; More attempts to achieve the desired result.

    Until True

    ; Code continues inside the function.
Edited by czardas

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I guess this is a little bit more readable than nested if statements, which most would do I guess (including me). I have seen your approach in the Crypt UDF by the way. Is it better? Actually I don't know if anything is wrong with it. I am stumped.


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The benefits of a GOTO statement without using a GOTO statement.  I find it very clever.

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#17 ·  Posted (edited)

I write lots of data validation routines that run several hundred validation checks on each row of data and I use the same sort of structure as sown in your first post. The alternative would be a ridiculous set of nested IFs or ElseIfs. The loop that never loops in combination with If False Then ExitLoop  statements is my opinion an elegant way to implement this for the following reasons:

  • It is clear to read and understand.
  • It is easy to add additional tests
  • The order of the tests is easy to change
  • It can be optimised by putting the tests most likely to fail at the top.
Edited by Bowmore
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#18 ·  Posted (edited)

Bowmore - Indeed there are some benefits to using a construct like this. My code posted above will require some optimization later. Tests need to be run for fine tuning etc... Working this way is easy. :)

Chimp - There's hardly any difference using a For loop. In fact the way I am doing this does not require the comparison of an incremented loop iteration count.

Thanks for all your responces. I would like to mark this solved, but there are a number of best answers here. I'll just pick one. :D

Edited by czardas

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#19 ·  Posted (edited)

I finally read the topic correctly,.I suppose I can see why this approach might suit some folk.

Personally I think Functions are as modular as I need. Depending how much code was in the tests, I might find it more difficult to follow.

Edited by JohnOne

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#20 ·  Posted (edited)

If the code did not sit so well, I would normally call another function. There are several other variables involved in the following part of the loop including an extended return value for the current function. Since the data is manipulated in various ways in an attempt to achive a single objective - the code belongs together in one place. Passing lots of ByRef parameters is the alternative.

Edited by czardas

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