From: Julian Leviston <julian@...>
Date: 2009-11-22T12:17:14+09:00
Subject: Re: really crazy about this (do/while)

My guess is because floats aren't exact, so adding .1 ten times isn't  
precisely the same as adding 1.

Use BigDecimal if you wanna be really accurate.

Julian

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On 22/11/2009, at 2:09 PM, Ruby Newbee <rubynewbee@gmail.com> wrote:

> Hello,
>
> Please see the code and running result below:
>
> #
> # case one
> #
> [root@localhost tmp]# cat t5.rb
> temp = 98.4
> i = 0
>
> begin
>  i += 1
>  puts "step" + i.to_s + " befre adding is " + temp.to_s
>  temp += 0.1
>  puts "step" + i.to_s + " after adding is " + temp.to_s
>  puts
> end while temp < 98.6
>
>
> [root@localhost tmp]# ruby t5.rb
> step1 befre adding is 98.4
> step1 after adding is 98.5
>
> step2 befre adding is 98.5
> step2 after adding is 98.6
>
>
> OK I think the result is pretty right.
>
> Now I change temp's original value to 98.3:
>
> #
> # case two
> #
> [root@localhost tmp]# cat t5.rb
> temp = 98.3
> i = 0
>
> begin
>  i += 1
>  puts "step" + i.to_s + " befre adding is " + temp.to_s
>  temp += 0.1
>  puts "step" + i.to_s + " after adding is " + temp.to_s
>  puts
> end while temp < 98.6
>
>
> [root@localhost tmp]# ruby t5.rb
> step1 befre adding is 98.3
> step1 after adding is 98.4
>
> step2 befre adding is 98.4
> step2 after adding is 98.5
>
> step3 befre adding is 98.5
> step3 after adding is 98.6
>
> step4 befre adding is 98.6
> step4 after adding is 98.7
>
>
> The output of step4 let me crazy.
> Why the loop doesn't break after step3?
> Because after step3 temp's value is 98.6, the loop condition was
> checked, and the loop should be end.
>
> Since I think case one is right, so case two get wrong result. Why?
> Thank you.
>