OpenEuphoria

RE: BUG! Erratic for loop behavior

• Posted by Andy Serpa <renegade at earthling.net> Mar 23, 2002
• 530 views

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....