Re: Want to delete item from list. Can't understand archived notes

[Piotr Sieniawski]

On Thu, 23 Jul 1998, Michael Whidden wrote:
> Paul E. Johnson wrote:
> 
> I'll answer in comments to each statement
> 
> > Now Just one more question.
> >   Sometimes while statements using indexes are written like this:
> >       while (( aRecruiter=[index next]))
> 
> Loops until the parenthesized expression is 'false'.  NULL is a
> 'false' value, and the value of a assignment (=) is the value of
> right-hand side.  So, when [index next] returns NULL, the while
> loop exits
> 
> >   and other times, by other people, they are written like this
> >       while (( [index next] != NULL)
> This does the same thing by an explicit comparison because,
> technically, on some systems (although, I've never seen one)
> NULL is not a false value itself.  Because [index next] is
> not assigned to anything, it is assumed you will retrieve
> the current list item via [index get] inside the loop.
> 
> >   and yet other times it is
> >       while (( aRecruiter = [index next] != NULL))
> This checks for NULL while assigning the next item
> to aRecruiter so you don't have to call [index get] 
> inside the while loop.
> 
> > Why these differences?  It seems to me the !=NULL is superfluous ?
> 
> Like I said above, supposedly, on some machines, NULL is not '0', and
> so may not be false.  (I think some old wierd architectures used 
> '-1' for NULL or something
> 

One more thing. 
You can use

while (aRecruiter=[index next])

or

while (aRecruiter=[index next] != NULL)

but what if some day by mistake you use

while (aRecruiter=bRecruiter)

instead of (aRecruiter==bRecruiter)

This typo is very hard to find. And if somebody else try to watch youre
code, he won't be sure if this is correct or wrote by mistake.


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