From: Mohit Sindhwani <mo_mail@...>
Date: 2010-02-22T02:50:20+09:00
Subject: Re: Yet another rounding issue

On 22/2/2010 1:39 AM, Manu Sankala wrote:
> At school I was taught that five is always rounded up. Later on I've
> been told that sometimes five is rounded to closest even number. Neither
> of these seem to be the case with ruby:
>
> irb(main):044:0>  RUBY_VERSION
> =>  "1.8.7"
> irb(main):045:0>  (217.5).round
> =>  218
> irb(main):046:0>  (218.5).round
> =>  219
> irb(main):047:0>  (2.175*100).round
> =>  217
> irb(main):048:0>  (2.185*100).round
> =>  219
> irb(main):049:0>  sprintf('%.2f',2.175)
> =>  "2.17"
> irb(main):050:0>  (2.175*100.0).round/100.0
> =>  2.17
>
> Can someone please tell me how do I round 2.175 to 2.18, besides
> ((2.175*100).to_s+'9').to_f.round/100.0 ?
>    

Actually, this is because of the way floating point variables are 
handled in a computer.

You could try:
a = 2.175
b = a + 0.0005
c = ((b * 100).round) / 100.0

irb(main):010:0> a = 2.175
=> 2.175
irb(main):011:0> b = a + 0.0005
=> 2.1755
irb(main):012:0> c = (b * 100).round / 100.0
=> 2.18
irb(main):013:0> a = 2.185
=> 2.185
irb(main):014:0> b = a + 0.0005
=> 2.1855
irb(main):015:0> c = (b * 100).round / 100.0
=> 2.19

Cheers,
Mohit.
22/2/2010 | 1:46 AM.