From: Gavin Kistner <gavin@...>
Date: 2005-09-01T10:16:23+09:00
Subject: Re: Time (leap year??)

On Aug 31, 2005, at 2:11 PM, csjasnoch@wisc.edu wrote:
> How does it work
> Every 4 years, every hundred but not every millenia.. Or is it also  
> not
> every 100?

"Every year divisible by 4 is a leap year.
But every year divisible by 100 is NOT a leap year
Unless the year is also divisible by 400, then it is still a leap year."
-- http://www.timeanddate.com/date/leapyear.html

So to calculate it on your own:
irb(main):001:0> def is_leap?( year ); year % 4 == 0 && ( year % 100 ! 
= 0 || year % 400 == 0 ); end
=> nil
irb(main):002:0> is_leap? 1996
=> true
irb(main):003:0> is_leap? 1997
=> false
irb(main):004:0> is_leap? 2000
=> true
irb(main):005:0> is_leap? 2100
=> false
irb(main):006:0> is_leap? 2300
=> false
irb(main):007:0> is_leap? 2400
=> true