| Re: Trouble with a loop [message #67674] |
Fri, 14 August 2009 07:02 |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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On Aug 14, 9:14 am, Allan Whiteford
<allan.rem...@phys.remove.strath.ac.remove.uk> wrote:
> David Baker wrote:
>> I'm hoping someone on here maybe able to help me with a problem i'm
>> having trying to construct the following type of loop
>
>> FOR i=0,end DO BEGIN
>> IF x GT y THEN BEGIN
>> FOR j=0,end DO BEGIN
>> some program statements
>> ENDFOR
>> end=end-1
>> b=b+1
>> i=i-1
>> ENDIF
>> ENDFOR
>
>> Now the problem i'm facing is that although the i value is correctly
>> changed IDL is unaware that the limits of the for loop have been
>> decrease (i,e the value end doesn't appear to be updated when checking
>> i against it for the for loop thus leaving me in a recurring loop.)
>
>> Does anyone have any advice/ideas?
>
>> Many thanks,
>> David
>
> David,
>
> Using a variable called "end" is a really bad idea from the start, it's
> a reserved word.
>
> That aside, you want a "while" construct rather than a "for" construct:
>
> i=0
> while i++ le endvar DO BEGIN
> IF x GT y THEN BEGIN
> FOR j=0,endvar DO BEGIN
> some program statements
> ENDFOR
> endvar=endvar-1
> b=b+1
> i=i-1
> ENDIF
> ENDFOR
>
> It's also poor form and a bit rude to change your loop variable inside
> of a for loop (i.e. your line saying i=i-1) although this is normally
> considered ok inside a while.
>
> I suspect you need to take a step back and ask what you're trying to do
> with this code. It's hard for us to tell because we don't know what
> "some program statements" are and how they relate to x and y. It looks
> to me like it's almost "endvar"/"end" which should be the loop variable.
>
> Hope this helps.
>
> Thanks,
>
> Allan
Also, alternatively, if you need end(var) to decrease,
in IDL you can do something like:
for k=10,1,-1 do stuff
This will make k take the values of 10, 9, ..., 2, 1
Ciao,
Paolo
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| Re: Trouble with a loop [message #67675 is a reply to message #67674] |
Fri, 14 August 2009 06:14  |
Allan Whiteford
Messages: 117
Registered: June 2006
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Senior Member |
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David Baker wrote:
> I'm hoping someone on here maybe able to help me with a problem i'm
> having trying to construct the following type of loop
>
> FOR i=0,end DO BEGIN
> IF x GT y THEN BEGIN
> FOR j=0,end DO BEGIN
> some program statements
> ENDFOR
> end=end-1
> b=b+1
> i=i-1
> ENDIF
> ENDFOR
>
> Now the problem i'm facing is that although the i value is correctly
> changed IDL is unaware that the limits of the for loop have been
> decrease (i,e the value end doesn't appear to be updated when checking
> i against it for the for loop thus leaving me in a recurring loop.)
>
> Does anyone have any advice/ideas?
>
> Many thanks,
> David
David,
Using a variable called "end" is a really bad idea from the start, it's
a reserved word.
That aside, you want a "while" construct rather than a "for" construct:
i=0
while i++ le endvar DO BEGIN
IF x GT y THEN BEGIN
FOR j=0,endvar DO BEGIN
some program statements
ENDFOR
endvar=endvar-1
b=b+1
i=i-1
ENDIF
ENDFOR
It's also poor form and a bit rude to change your loop variable inside
of a for loop (i.e. your line saying i=i-1) although this is normally
considered ok inside a while.
I suspect you need to take a step back and ask what you're trying to do
with this code. It's hard for us to tell because we don't know what
"some program statements" are and how they relate to x and y. It looks
to me like it's almost "endvar"/"end" which should be the loop variable.
Hope this helps.
Thanks,
Allan
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