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Re: How to change the increment of FOR loop? [message #65589]

Thu, 12 March 2009 05:24

Allan Whiteford
Messages: 117
Registered: June 2006

Senior Member

Fï¿½LDY Lajos wrote:
>
> On Wed, 11 Mar 2009, Hu wrote:
>
>> Hi, there
>> I got a question relating to the variational increment of FOR
>> Statement. I used the code like this:
>> ;;; begin
>> increment =20
>> FOR j = 0, N-1, increment DO BEGIN
>> IF a gt 0 THEN BEGIN
>> ;......
>> increment=10
>> ENDIF ELSE BEGIN
>> ;......
>> increment=12
>> ENDELSE
>> ENDFOR
>> ;; end
>>
>> But the increment have not changed according to IF... ELSE ...
>> statement..
>> What I want is to change the increment according to different
>> conditions. that is, if variable a is greater than 0, the increment of
>> the FOR loop will be 10 , not its default value 20.....
>>
>> Is there any solution to this problem?
>
>
> increment is evaluated only once, before the loop starts (and it is
> copied to a temporary variable you can not reach). You have to create a
> loop manually:
>
> j=0
> increment=20
> while 1 do begin
>
> IF a gt 0 THEN BEGIN
> ;......
> increment=10
> ENDIF ELSE BEGIN
> ;......
> increment=12
> ENDELSE
>
> j=j+increment
> if j ge n then break
>
> endwhile
>
>
> regards,
> lajos

Although probably something like:

j=0
increment=20
while ((j+=increment) lt n) do begin

IF a gt 0 THEN BEGIN
;......
increment=10
ENDIF ELSE BEGIN
;......
increment=12
ENDELSE

endwhile

is easier to recognise as a "loop" from the point of view of
understanding the code later for maintenance.

Thanks,

Allan

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[Message index]

		Re: How to change the increment of FOR loop? By: Allan Whiteford on Thu, 12 March 2009 05:24
		Re: How to change the increment of FOR loop? By: Hu on Wed, 11 March 2009 14:42
		Re: How to change the increment of FOR loop? By: Foldy Lajos on Wed, 11 March 2009 14:24
		Re: How to change the increment of FOR loop? By: Foldy Lajos on Fri, 13 March 2009 03:31

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