For loop using variable step.

[jassing]

I was surprised I could not do this:

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For i = 1 To Len(cString) Step nBreak

Wishlist is to allow step to allow a dynamic runtime set value, ok if it becomes 'static' after initial use. (ie: nBreak shouldn't change once the for loop is started)

[ts-soft]

This was discussed at many Time.
The step is a fix value, it is set on compiletime, not at runtime. You can use a constant.
If Fred change this, the for:next is slower and can't optimized.

Why not use While : Wend or Repeat : Until.

[Tenaja]

There are some additional options here:
http://purebasic.fr/english/viewtopic.p ... 6&p=360605

[Seymour Clufley]

And, IIUC, that code is inefficient because it will re-check the length of the string which each iteration of the loop. You should put it in a variable first.

[Nituvious]

What about something like this:

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myStep = 1
While (i<=15 - myStep): i + myStep
	
	If i = 5 : myStep = 5 : EndIf
	
	Debug "Loop count: " + Str(i)

Wend

[edit] oops, sorry. Looks like the linked thread already discusses this.

[Lord]

This was discussed at many Time.
The step is a fix value, it is set on compiletime, not at runtime. You can use a constant.
If Fred change this, the for:next is slower and can't optimized.

Why not use While : Wend or Repeat : Until.

If I remember correctly, Fred suggested something like this:

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A.f=1
E.f=10
myStep.f=0.5
For i=A To E Step 0
;Do whatever you want to do  
  Debug i
  i+myStep
Next

But I think, this is not the answer to the original question.

[Josh]

Code: Select all

For i = 1 To Len(cString)

To use Len in a loop can quickly end in a disaster. Ok, if it's a short string, you will not check it. But for each doubling the len of the string, the running time will be about four times longer.

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cString.s = Space (10000) ;test also with 20k and 40k

time = ElapsedMilliseconds()

For i = 1 To Len(cString)
  x = 1
Next

MessageRequester ("", Str (ElapsedMilliseconds() - time))

[MachineCode]

Josh is right. You don't call Len() repeatedly if the size doesn't change. Calc it once, and use that value in the For/Next loop. In Josh's example above, and using Space(40000), the loop takes 700 ms on my PC. But if I calc Len() first and use that value in the loop, the code executes in 0 ms (instantly).

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cString.s = Space (40000) ; 40k

time = ElapsedMilliseconds()

l=Len(cString)

For i = 1 To l
  x = 1
Next

MessageRequester ("", Str (ElapsedMilliseconds() - time))