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For loop using variable step.
Posted: Sun Sep 30, 2012 8:21 pm
by jassing
I was surprised I could not do this:
Code: Select all
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)
Re: For loop using variable step.
Posted: Sun Sep 30, 2012 8:36 pm
by 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.
Re: For loop using variable step.
Posted: Sun Sep 30, 2012 9:20 pm
by Tenaja
Re: For loop using variable step.
Posted: Mon Oct 01, 2012 6:33 pm
by 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.
Re: For loop using variable step.
Posted: Thu Oct 04, 2012 7:58 pm
by Nituvious
What about something like this:
Code: Select all
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.
Re: For loop using variable step.
Posted: Fri Oct 05, 2012 8:15 am
by Lord
ts-soft wrote: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:
Code: Select all
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.
Re: For loop using variable step.
Posted: Fri Oct 05, 2012 7:05 pm
by Josh
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.
Code: Select all
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))
Re: For loop using variable step.
Posted: Sat Oct 06, 2012 3:29 am
by 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).
Code: Select all
cString.s = Space (40000) ; 40k
time = ElapsedMilliseconds()
l=Len(cString)
For i = 1 To l
x = 1
Next
MessageRequester ("", Str (ElapsedMilliseconds() - time))