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newbie question

Will Hall

10/7/2008 10:27:00 PM

[Note: parts of this message were removed to make it a legal post.]

Greetings all, I think this is generally more a programming question than a
ruby explicit one, however, I am wondering why this code yields 23,
0.999999999999979 instead of 23, 1.

Any help would be great!

i = 0
while i <= 50
a = 37*i / 50
c = a + 0.0
b = (37*i/50.0 - c ) *50
if b < 1.5 && b > 0.5
puts i
puts b
end
i = i+1
end


thanks much
Will
3 Answers

Farrel Lifson

10/7/2008 10:45:00 PM

0

Rounding errors in floating point arithmetic.

Farrel

On 08/10/2008, Will <wrsh07@gmail.com> wrote:
> Greetings all, I think this is generally more a programming question than a
> ruby explicit one, however, I am wondering why this code yields 23,
> 0.999999999999979 instead of 23, 1.
>
> Any help would be great!
>
> i = 0
> while i <= 50
> a = 37*i / 50
> c = a + 0.0
> b = (37*i/50.0 - c ) *50
> if b < 1.5 && b > 0.5
> puts i
> puts b
> end
> i = i+1
> end
>
>
> thanks much
> Will
>


--
Aimred - Ruby Development and Consulting
http://www....

Tim Hunter

10/7/2008 11:08:00 PM

0

Will wrote:
> Greetings all, I think this is generally more a programming question than a
> ruby explicit one, however, I am wondering why this code yields 23,
> 0.999999999999979 instead of 23, 1.
>

A common question. Check out http://en.wikipedia.org/wiki/Floa....

--
RMagick: http://rmagick.ruby...

Todd Benson

10/8/2008 1:08:00 AM

0

On Tue, Oct 7, 2008 at 5:27 PM, Will <wrsh07@gmail.com> wrote:
> Greetings all, I think this is generally more a programming question than a
> ruby explicit one, however, I am wondering why this code yields 23,
> 0.999999999999979 instead of 23, 1.
>
> Any help would be great!
>
> i = 0
> while i <= 50
> a = 37*i / 50
> c = a + 0.0
> b = (37*i/50.0 - c ) *50
> if b < 1.5 && b > 0.5
> puts i
> puts b
> end
> i = i+1
> end

require 'bigdecimal'

#put a bigdecimal in the numerator or denominator...
((BigDecimal("37") * 23 / 50 - 17) * 50).to_f
#=> 1.0

Todd