From: Axel Etzold <AEtzold@...>
Date: 2008-09-16T00:41:33+09:00
Subject: Re: how do deal with huge numbers and keep them accurate?


-------- Original-Nachricht --------
> Datum: Tue, 16 Sep 2008 00:34:15 +0900
> Von: "Todd Benson" <caduceass@gmail.com>
> An: ruby-talk@ruby-lang.org
> Betreff: Re: how do deal with huge numbers and keep them accurate?

> On Mon, Sep 15, 2008 at 9:36 AM, Tomi Zzzz <tomi_z@nana.co.il> wrote:
> > thanks u all for taking a few minutes to answer me. I'm really
> > embarrassed cause I wanted to simplify the question so, I didn't wrote
> > down the actual code. I also sorry for not posting any answer yesterday.
> > so once more, your help would be very much appreciate...
> >
> > (I'll drop the 3 lines at the beginning cause I don't sure about them,
> > and don't want to mislead you. (talking about: include... require...
> > etc).
> >
> > this is what i want to achieve with that code:
> >
> > number = gets.chomp.to_f
> > divider = 3.0
> > while number % divider != 0
> > divider += 1.0
> > end
> > puts divider.to_s
> > if divider == 3.0
> >  puts "the number can be divided by " + divider.to_s
> > else
> >  puts "can't be divided"
> > end
> >
> > that's it. sorry for repeating myself... once more:
> > i want the ability to input a number like this:
> > 333333333333333333333333333333331
> > we all know that the answer will be something like that:
> > 1111.....111.333333
> > but the code will give me the answer that it can be divide by 3, and
> > that's the main problem in that code.
> >
> > Thanks in advanced, Tomiz.
> > p.s. i have tried to implement all of your suggestions with no luck.
> > I've add the code for your comfort.
> 
> Once again, you are using floats...
> 
> irb(main):001:0> require 'bigdecimal'
> => true
> irb(main):002:0> n = Bigdecimal('333333333333333333333333333333331')
> => #<BigDecimal:b7cf7418,'0.3333333333 3333333333 333333333 331E33,36(40)>
> irb(main):003:0> d = Bigdecimal('3')
> => #<BigDecimal:b7d08754,'0.3E1',4(8)>
> irb(main):004:0> (n % d).to_f
> => 1.0
> 
> Looks fine to me.
> 
> Todd


Dear Tomi,

as Todd said, using Float is the problem.. Of course you can divide any Float by any other Float (excluding 0.0).
But you could do the following, e.g., 

axel@alecrim:~$ irb
irb(main):001:0> a=122222222222222222222222222222222222222
=> 122222222222222222222222222222222222222
irb(main):002:0> b=333333333333333333
=> 333333333333333333
irb(main):003:0> a%b
=> 111111111111111233
irb(main):004:0> a.class
=> Bignum
irb(main):005:0> b.class
=> Bignum
irb(main):006:0> 

Conversions are automatic there, ie. b=3 would be a Fixnum.
Number a will be divisible by b if a%b==0.

Best regards,

Axel 


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