OpenEuphoria

Re: BUG! Erratic for loop behavior

• Posted by Dan Moyer <DANIELMOYER at prodigy.net> Mar 24, 2002
• 486 views

Andy,

Got it.  I think Kat made a suggestion once for doing "string math" to avoid
this problem in general, don't remember if there was a problem or downside
other than speed.  If it's always/only add/subtract dollars & cents, though,
mult/divide
everything that's dollars by 100 should work, but multiplication (like but
not limited to percents) could become a problem, as Chris pointed out that
my solution won't
work for 7 places to right of decimal (his mod of his method works up to 9 I
think).

And I agree that this should be mentioned in the manual, you caught it in
time, others might not, although that brings up the question "who reads the
fine manual?".  :)
(actually I refer to it constantly, but that's bad memory at work!)

Dan

----- Original Message -----
From: "Andy Serpa" <renegade at earthling.net>
To: "EUforum" <EUforum at topica.com>
Sent: Saturday, March 23, 2002 10:24 PM
Subject: RE: BUG! Erratic for loop behavior


>
>
> Dan Moyer wrote:
> > Andy,
> >
> > Although I assume this is at least obvious, you could just do this:
> >
> > for i = 10*31.1 to 10*34.2  do
> >   ?i/10
> > end for
> >
> > Same for whatever max "level" of floating point you have, ie, if *any*
> > value
> > goes out to .001,multiply all by 1000, then divide, etc.
> >
>
> > Maybe there's some good reason that doesn't occur to me offhand why this
> > won't work?
> >
>
> No, that works fine for getting this particular loop to work.  But the
> problem outside of a loop as well.  Let's say you make an application
> that adds and subtracts dollars & cents a lot.
>
> .1 + .1 + .1 + .1 + .1 + .1 + .1 + .1 + .1 does not equal 1 -- just try
> it.  It will display as one if you print it, but if you do this:
>
> x = .1 + .1 + .1 + .1 + .1 + .1 + .1 + .1 + .1
> if x = 1 then
>   puts(1,"TRUE.")
> else
>   puts(1,"FALSE.")
> end if
>
> It will come up false.
>
> So if you have a program that does any kind of floating-point
> calculations, and then check to see if a particular value = some other
> value, you'll often get the wrong answer.
>
> I just didn't realize before it was so serious.  Those of use who don't
> come from a low-level programming background or don't have a lot of
> hardware knowledge aren't told this anywhere.  It really ought to be in
> the manual....
>
>
>
>