Ruby Forum Ruby > Help with leap year programing

Hi, All,

I am a beginner on programming now reading books by Chris Pine: Learn
to Program.
On chapter 6, I got same assignment. I guess that is a classic one.

I have tried to use what I have learned so far: The loop.

My code is as below. i have run several test without finding any
problem.

Can you help to have a look and throw some light on any possible
improvement? Thanks.

____________________

puts 'starting year:'
s = gets.chop
puts 'ending year:'
e = gets.chop

if s.to_i > e.to_i
  puts 'ending year should be bigger than staring year'
  else
    puts 'leap year between ' + s + ' and '+ e + ' as below:'
end

while s.to_i  < e.to_i

  while ( (s.to_i % 4 == 0 and s.to_i % 100 != 0) or (s.to_i % 100 ==
0 and s.to_i % 400 == 0 ))
      puts s
      s = s.to_i + 1
      end
s = s.to_i + 1
end
puts 'all done'


On Nov 7, 2006, at 12:15 PM, Shiloh Madsen wrote:


> 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

On 01.09.2007 16:33, HB wrote:
> improvement? Thanks.
The fist thing I'd change is to remove all the #to_i's.  You should
convert to integer just once, namely after reading user input.  If you
use Integer() for the conversion, then you also get automatic error
checking, i.e., if the user enters "foo" no calculations will be done
but he will see an error message instead.

Next, I am not sure what you are trying to achieve.  As far as I can see
there is no condition on the "puts s" but your print statement seems to
indicate that you are interested in leap years only.  If you want to
print leap years only then you need to somehow put a condition around
that output statement.

Normally you would need just a single loop as far as I understand the
problem and what you are trying to do.  So you could get rid of one of 
them.

I would also move the leap year output code inside the if-else.  The
code will likely work the way it is as well because if s>e the body of
the while loop will never be executed.  But from a control flow point of
view the code becomes clearer when you nest the "activity" (leap year
calculation and output in this case) in the proper branch of the
conditional statement.

>     puts 'leap year between ' + s + ' and '+ e + ' as below:'
> end
> puts 'all done'

Kind regards

  robert

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* HB:

> On chapter 6, I got same assignment. I guess that is a classic one.

So here is a nonclassic solution to this classic problem :)

If s % 4 differs from 0 we start with a year that cannot be a leap year.
If this occurs add 4 - (s % 4) to skip to the next year that is a leap
year unless century rules happen to apply. Now only every fourth year
needs to be considered. A year that can be divided by four is a leap
year under the condition that it can be divided by 400 or cannot be
divided by 100.

puts 'starting year:'
s = gets.chomp.to_i
puts 'ending year:'
e = gets.chomp.to_i

if s > e
    puts 'ending year should be bigger than staring year'
else
    puts "leap year between #{s} and #{e} as below:"
end

s += 4 - (s % 4) if s % 4 != 0

while s  <= e
    puts s if (s % 400 == 0 or s % 100 != 0)
    s += 4
end
puts 'all done'

Josef 'Jupp' Schugt
- --
Blog available at http://www.mynetcologne.de/~nc-schugtjo/blog/
PGP key with id 6CC6574F available at http://wwwkeys.de.pgp.net/
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HB wrote:
> Hi, All,
> 
> I am a beginner on programming now reading books by Chris Pine: Learn
> to Program.
> On chapter 6, I got same assignment. I guess that is a classic one.
> 
> I have tried to use what I have learned so far: The loop.
> 
> My code is as below. i have run several test without finding any
> problem.
> 
> Can you help to have a look and throw some light on any possible
> improvement? Thanks.
> 

I think it's easier to use Date#leap? for this question.

puts 'Starting year:'
start = gets.chop
puts 'Ending year:'
ending = gets.chop
if start.to_i > ending.to_i
  puts 'Ending year should be bigger than staring year'
else
   puts 'Leap year between ' + start + ' and '+ ending + ' as below:'
   while start.to_i <= ending.to_i
    if Date.new(start.to_i).leap?
      puts start
    end
    start = start.to_i + 1
  end
end
puts 'all done'


Yoi

On Sep 3, 12:24 am, Hu Yoi <kgo_...@hotmail.com> wrote:
> > problem.
> if start.to_i > ending.to_i
> puts 'all done'
>
> Yoi
> --
> Posted viahttp://www.ruby-forum.com/.

Thanks to all!
I have a lot to learn and it is fun!

HB wrote:
> Hi, All,
> 
> I am a beginner on programming now reading books by Chris Pine: Learn
> to Program.
>
> ...
>
>     while ( (s.to_i % 4 == 0 and s.to_i % 100 != 0) or (s.to_i % 100 ==
>           0 and s.to_i % 400 == 0 ))
>
> 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


Your complex conditional can be expressed more clearly with a series of 
if statements:

start = 2000
finish = 2200

year = start

while year <= finish

    is_leap =
        if year % 400 == 0
            true
        elsif year % 100 == 0
            false
        else
            year % 4 == 0
        end

    if is_leap: puts year
    end

    year += 1
end



Or you can use each() on a Range for your loop, and a case statement 
inside the loop:

start = 2000
finish = 2200

user_range = start..finish

user_range.each do |year|

    is_leap =
        case
        when year % 400 == 0
            true
        when year % 100 == 0
            false
        else
            year % 4 == 0
        end

    if is_leap: puts year
    end

    year += 1
end