From: Robert Klemme <bob.news@...>
Date: 2005-03-31T23:35:04+09:00
Subject: Re: Integer/Float oddity


<horati0@linuxmail.org> schrieb im Newsbeitrag
news:1112277873.331258.267880@f14g2000cwb.googlegroups.com...
> not really an oddity, more a lack of understanding on my part regarding
> ruby's internal type conversion...
>
> (100*(1.15-1))
> => 15.0
>
> (100*(1.15-1)).to_int
> => 14
>
> (100*(1.15-1)).to_int.round
> => 15
>
> 15.0.to_int
> => 15
>
> what am i missing here?  i never would have thought to use .round to
> get the 'correct' result unless someone told me.  by correct i mean if
> i was doing this with a paper and pencil, i would expect to get 15, not
> 14.
>
> any insight would be appreciated, especially a way (if possible) to
> override this behaviour so i dont run into this in the future.
>
> thanks,
> horati0

This is a typical limitation of numeric calculations.  The reason for what
you see is that 1.15-1 is smaller than 0.15:

>> (1.15-1) - 0.15
=> -8.32667268468867e-17

consequently

>> (100 * (1.15-1))-15
=> -8.88178419700125e-15

this is negative => (100 * (1.15-1)) is smaller than 15 and thus it's
correctly converted to 14 by to_int.

Kind regards

    robert