Strange behavior of a very simple script

[VenusProject2]

Do
    For $q = 1 to 7
        MsgBox(0,"ForLoop", " $q = " & $q)
    Next
        MsgBox(0,"DoLoop", " $q = " & $q); Why does $q=8 here?
Until $q = 7

$q is incremented from 7 to 8 when finishing the "For/Next" loop, I do not understand why. Can anyone explain this I'm baffled?

[JohnOne]

I do not know, but I know that a variable like that should not be used outside the loop it is intended for.

[VenusProject2]

Good point John, but it's kind of Twilight Zone behavior that is troubling wouldn't you say?

This worked....

Do
    For $q = 1 to 7
        MsgBox(0,"ForLoop", " $q = " & $q)
        $k = $q
    Next
        MsgBox(0,"DoLoop", " $q = " & $q); Why does $q=8 here?
Until $k = 7

Edited September 8, 2014 by VenusProject2

[232showtime]

still the same.....

[JohnOne]

I would say it is actually a bug, but someone would come along and say otherwise so let's just say using such a temp variable outside of its loop causes undefined behaviour.

I imagine it has something to do with how AutoIt handles loops, and specifically nested loops.

You see the Until keyword does not recognize that the variable has reached its limit and Do loop should end.

[mikell]

Hypothesis :

$q is created automatically with Local scope, the start value is 1, the stop value is 7, the step value is 1

Then the For loop tests $q, then increments it, then tests again
7 = stop value  then  $q = 7 is accepted
8 > stop value  then  $q = 8 causes an exitloop
This means that the 8 value (stop value + step value) must be tested

It works with $k = 7 because the tested var is $q, not $k
 

[VenusProject2]

Yes John until otherwise resolved, "using such a temp variable outside of its loop causes undefined behaviour".

232showtime yes still the same disturbing behavior but the work around got the script to work as I needed, albeit with some unnecessary complexity...

[jchd]

There is nothing close to a bug there, just basic careless code.

[VenusProject2]

Thanks mikell that explains the behavior, science saves me from believing in something mystical again

Hypothesis :

$q is created automatically with Local scope, the start value is 1, the stop value is 7, the step value is 1

Then the For loop tests $q, then increments it, then tests again
7 = stop value  then  $q = 7 is accepted
8 > stop value  then  $q = 8 causes an exitloop
This means that the 8 value (stop value + step value) must be tested

It works with $k = 7 because the tested var is $q, not $k
 

[VenusProject2]

Do
    For $q = 1 to 7
        MsgBox(0,"ForLoop", " $q = " & $q)
    Next
        MsgBox(0,"DoLoop", " $q = " & $q)
Until $q = 8

This is will do nicely

[JohnOne]

I'm not sure I'd accept the answer you did unless I heard it from a code dev.

Why would the local var need to be tested again? it is equal to 7 and tested at the top of the loop, it is not While $var < 8 where it might be tested.

[jchd]

What is the purpose the outer Do loop?

[232showtime]

I'm not sure I'd accept the answer you did unless I heard it from a code dev.

Why would the local var need to be tested again? it is equal to 7 and tested at the top of the loop, it is not While $var < 8 where it might be tested.

yeah you are rigth, its kinda strange script...

EDIT: Waiting for a Dev. to show up... >_<

Edited September 8, 2014 by 232showtime

[kylomas]

Run it like this and get the same result...

;Do
    For $q = 1 to 7
        MsgBox(0,"ForLoop", " $q = " & $q)
    Next
    MsgBox(0,"DoLoop", " $q = " & $q); Why does $q=8 here?
;Until $q = 7

So the question might be "how is the increment variable being handled?"

[mikell]

JO, please note that I said Hypothesis

Though I'm totally ignorant about how the internal engine works, I can't imagine the way the For loop will 'know' when to exitloop without doing some kind of internal test or comparison

My hypothesis is certainly simplistic but tries to find a rational answer 

For $q = 1 to 7
     MsgBox(0,"ForLoop", " $q = " & $q)
    ; If $q = 7 Then Exitloop
Next
MsgBox(0,"", " $q = " & $q)

Edit

Obviously the Do...Until $q...  in this case is bad practice (and redundant)

Edited September 8, 2014 by mikell

[JohnOne]

I'm not knocking the answer, It's an answer like anyone else's, just saying I would not accept it as the definitive answer.

If you tried to use a variable like that in C/++ it will not allow you..

for (int i = 0; i <= 7; i++)
        {
            // blah
        }
 cout << i;

It will error, so there is obviously some handling going on, and only an AutoIt code dev can really say whether this issue is intended or a bug.

[Gianni]

always seen this behavior in "for next" loops, also in other basic languages.
This is the normal behavior of the "for next" loop.
If you read well the documentation, is also clearly written there:
"The For loop terminates when the value of variable exceeds the stop threshold."

[kylomas]

Nice, chimp....K.I.S.S.

[JohnOne]

Anyway, a workaround might be...

Do
    For $q = 1 to 7
        MsgBox(0,"ForLoop", " $q = " & $q)
    Next
        MsgBox(0,"DoLoop", " $q = " & $q); Why does $q=8 here?
Until $q > 6

[mikell]

"The For loop terminates when the value of variable exceeds the stop threshold."

 

So my philistine hypothesis was finally not so wrong