From: dblack@...
Date: 2006-11-08T05:33:11+09:00
Subject: Re: Help with a program to determin leap years.

Hi --

On Wed, 8 Nov 2006, Shiloh Madsen wrote:

> So, I'm trying to go through the Teach Yourself Programming book by
> Pragmatic Press and I am encountering a few hurdles. The chapter I am
> working on now is asking me to create a program which will ask for a
> start and end year and then calculate all leap years in that range.
> The logic behind leap years (for those who need a refresher) is all
> years divisible by for are leap years EXCEPT those that are divisible
> by 100 UNLESS they are also divisible by 400. I am somewhat at a loss
> for how to handle the logic for this...finding all numbers that are
> divisible by 4 and removing those divisible by 100 is easy. Its adding
> in that third condition which adds some of the removed numbers back
> into the "true" group that I am having trouble with...or maybe I am
> just not wrapping my mind around the problem well
> enough...suggestions?

require 'date'
Date.leap?(year)   # :-)

See Morton's implementation.  Here, just for fun, is another:

   def leap?(year)
     year % 4 == 0 unless (year % 100 == 0 unless year % 400 == 0)
   end

It returns nil/true rather than false/true, so it's a bit
non-slick.  But I thought the semantics might be interesting.


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org