From: Patrick Hurley <phurley@...>
Date: 2005-03-31T23:26:31+09:00
Subject: Re: Integer/Float oddity

On Thu, 31 Mar 2005 23:09:46 +0900, horati0@linuxmail.org
<horati0@linuxmail.org> wrote:
> 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
> 
> 

Two quick notes - I think you meant 
> (100*(1.15-1)).round.to_int
> => 15

See if this clears anything up:
printf("%.15f", (100*(1.15-1)))
14.999999999999991=> nil

The result is not really 15, but just really really close, due to the
imprecision of floats - always round moving to ints - to_i is a
"floor" function. Similarly be very careful when comparing floats.

Patrick