From: Pit Capitain <pit@...>
Date: 2007-03-15T02:14:32+09:00
Subject: Re: Calculating the age given DOB

Brian Adkins schrieb:
> Reid Thompson wrote:
>> irb(main):001:0> require 'date'
>> => true
>> irb(main):002:0>  bd = Date.new(1966, 1, 21)
>> => #<Date: 4878293/2,0,2299161>
>> irb(main):003:0>  today = Date.new(2007,3,14)
>> => #<Date: 4908347/2,0,2299161>
>> irb(main):004:0>  age = today.year - bd.year
>> => 41
> 
> Consider when today.month < bd.month - you'll have an off-by-one error.

   age -= 1 if today.month < bd.month || today.month == bd.month && 
today.day < bd.day

I don't know how people born at February 29th celebrate their birthday 
in non-leap years. The code above makes them one year older on March 1st.

Regards,
Pit