[no need] For/Next: Set the countvariable to the last value

[Kurzer]

The For / Next loop ist really strange in PB.

When the For/Next loop is completely pass through, the counting variable is set to the "to-value" + 1

If you write:

Code: Select all

For i = 0 To 10
  ; Do something
Next i

The value of variable i will be 11 after exiting the For/Next loop.

Constructs like this one will beginners drive crazy

Code: Select all

  For i = 0 To 10
    Debug Str(i) + " / " + Str(j)
    For j = 0 To 10
    	; Do something other
    Next j
  Next i

For my understanding For/Next should set the counting value to the "to-value" after leaving the loop - in this example set to 10 instead of 11.

Edit: Edited the subject line to [no need]

[STARGÅTE]

-1

The loop current work properly!
For: Next is a head-controlled loop

And it works like any head-controlled loop

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Define i.i = 0
While i <= 10
 i + 1
Wend
Debug i

If you want it otherwise, use Repeat: Unitl, or a break!

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Define i.i = 0
Repeat
 i + 1
Until i >= 10
Debug i

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Define i.i
For i = 0 To 10
 If i = 10 : Break : EndIf
Next
Debug i

the loop may not at all accept the to-value, because this would not always be reached!

Code: Select all

Define i.i
For i = 0 To 10 Step 50
Next
Debug i

10 here would be to issue false


AND, all other languages are work same like PB, here JS:

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<script language="JavaScript">
for(n=0;n<=10;n++) ;
alert(n);
</script>

11

[Demivec]

For my understanding For/Next should set the counting value to the "to-value" after leaving the loop - in this example set to 10 instead of 11.

From my experience almost all programming languages do not define the value that the loop-counter-variable (LCV) should have after a loop exits. A beginner should never depend on the LCV being set to any particular value and an expert should likewise avoid doing so.

Just to show you what I mean, you say the LCV will equal the "to-value" + 1 after the loop exits, but look at this:

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For i = 10 To 0 Step - 1
  j = i
Next
Debug "Last value of loop: " + Str(j)
Debug "Value of LCV after loop: " + Str(i)

And if you have that one figured out what about this one:

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For i = 10 To 0 Step - 3
  j = i
Next
Debug "Last value of loop: " + Str(j)
Debug "Value of LCV after loop: " + Str(i)

As STARGÅTE pointed out the loop may not even be executed.

The LCV is for the loop only and not for use after the loop without setting its value explicitly. Of course beginners and non-beginners alike will still attempt to do so but it's not a good idea.

[Kurzer]

Code: Select all

j = 10
For i = 10 To 0 Step - 1
  j = i
Next
Debug "Last value of loop: " + Str(j)

Amazing!

Well now I understand. I never thought about a LCV at this level of detail.
Thank you Demivec and Stargate.

[PB]

> When the For/Next loop is completely pass through, the counting variable is set to the "to-value" + 1

Yep, just like in every other Basic that I've used. PureBasic is no different.