| Re: IDL FOR Loop variable increments [message #62591 is a reply to message #62583] |
Fri, 19 September 2008 12:09   |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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R.G. Stockwell wrote:
> "Jean H" <jghasban@DELTHIS.ucalgary.ANDTHIS.ca> wrote in message
> news:gauiil$u32$1@news.ucalgary.ca...
> ...
>> Could you comment on the "risk" of changing the loop counter within the
>> loop?
>
> my 2 cents.
>
> First, it is in changing the counter of a for loop.
> A for loop explicitly outlines what all counter variables will be.
>
> There are two things:
>
> 1) infinite loop, one could easily change the counter to never
> reach the end condition. A (valid) for loop will always reach the end
> condition.
>
> 2) more insidious, you could inadvertantly cast the counter to a float from
> an int, and then have one extra (and unintended ) statement executed.
This seems not to be possible in IDL, as loop counters, unlike normal
variables, cannot change their type.
Ciao,
Paolo
>
> instead of 0,1,2,3,4,5,6 (and not executing i = 7) you could get
> 0,1,2,3,4,4.99999999,5.99999,6.99999999, (and effectively executing the
> extra i ~ 7 step).
>
> Cheers,
> bob
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