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?
Here is simple way:
1. Write a is_leap? method.
def is_leap?(y)
return true if y % 400 == 0
return false if y % 100 == 0
return true if y % 4 == 0
false
end
2. <range>.select { |y| is_leap?(y) }
For example,
(1895..1905).select { |y| is_leap?(y) } # => [1896, 1904]
(1995..2005).select { |y| is_leap?(y) } # => [1996, 2000, 2004]
Regards, Morton
···
On Nov 7, 2006, at 12:15 PM, 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?
Hi --
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
···
On Wed, 8 Nov 2006, Shiloh Madsen wrote:
--
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] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org
The key point of all the methods proposed in this thread is: deal with the years divisible by 400 first, the years divisible by 100 second, and the years divisible by 4 last of all.
Regards, Morton
···
On Nov 7, 2006, at 12:15 PM, 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?
* Morton Goldberg, 11/07/2006 09:09 PM:
1. Write a is_leap? method.
def is_leap?(y)
return true if y % 400 == 0
return false if y % 100 == 0
return true if y % 4 == 0
false
end
YAWOFOIAYIALY:
def is_leap?(y)
return true if y % 400 == 0
return false if y % 100 == 0
return y % 4 == 0
end
Jupp
- --
YAWOFOIAYIALY: Yet another way of finding out if a year is a leap year.
You can fix that with the fun !! trick to convert nils back to false:
def leap?(year)
!!(year % 4 == 0 unless (year % 100 == 0 unless year % 400 == 0))
end
···
On 11/7/06, dblack@wobblini.net <dblack@wobblini.net> wrote:
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)
endIt returns nil/true rather than false/true, so it's a bit
non-slick. But I thought the semantics might be interesting.
AH! i was looking at it wrong...startin from validating divisible by 4
is the wrong direction...thank you all. I think I can make it work now
(many of you posted rather more advanced ways to do it. I am trying to
stick within the confines of the chapters ive done so far). Basically
I needed the way to approach the problem. Thanks all!
S.
···
On 11/7/06, Morton Goldberg <m_goldberg@ameritech.net> wrote:
On Nov 7, 2006, at 12:15 PM, 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?The key point of all the methods proposed in this thread is: deal
with the years divisible by 400 first, the years divisible by 100
second, and the years divisible by 4 last of all.Regards, Morton
what about small optimization (just for fun);
it works faster in most cases - non leap year happens more often:
def leap?(y)
(y%4).zero? && !(y%100).zero? || (y%400).zero?
end
sergey
···
----- Original Message ----- From: <dblack@wobblini.net>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Tuesday, November 07, 2006 3:33 PM
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)
endIt 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] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org
dblack@rubypal.com [mailto:dblack@rubypal.com]:
# year % 4 == 0 unless (year % 100 == 0 unless year % 400 == 0)
heheh thanks, this one should go to my bag of tricks, a (first) example of cascading unlesseses 
kind regards -botp