Re: [Dev-C++] Why don't you ever compare floats for equality?

[Daniel G. <sp...@ho...>]

Many thanks, that is a great explanation!





>From: Per Westermark <pw...@ia...>
>To: Daniel Glenfield <sp...@ho...>
>CC: dev...@li...
>Subject: Re: [Dev-C++] Why don't you ever compare floats for equality?
>Date: Thu, 9 Jan 2003 15:08:33 +0100 (CET)
>
>Because ((1.0 / 3.0) * 3.0) == 1.0 isn't guaranteed to be true because of
>round-off errors in evaluation.
>
>Floating point nubmers are able to store a number of significant digits -
>about 7-8 for float and 15 for double. However, only some numbers are
>possible to store exactly in a floating point variable. Most values are
>only possible to store as approximations, i.e. rounded or truncated to the
>number of available significant digits.
>
>You need an infinite number of digits to store the value 1/3 for example.
>Also, note that while we normally think of our floats and doubles as
>decimal values, they are stored in binary format in the computer,
>resulting in conversion errors when switching number base, i.e. when
>reading in or printing a number.
>
>/Per W
>
>On Thu, 9 Jan 2003, Daniel Glenfield wrote:
>
> > I read that you should never compare floating point numbers for 
>equality. I
> > was wondering why?
> >
> >
> >
> >
> >
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