From: Adam Prescott <mentionuse@...>
Date: 2011-01-29T00:59:02+09:00
Subject: Re: Each Array Method Skipping first Array position

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The answer is that your code doesn't take into account the situation where
the year is divisible by 4 and 100, but not divisible by 400:

>> [1800 % 4, 1800 % 100, 1800 % 400]
=> [0, 0, 200]

As a suggestion, you might want to make your range of years a range of
numbers, to prevent having to call to_i on them when using %. You can use
interpolated strings and Ruby will convert the numbers to a string for you.

Here's a re-indented, neatened up (in my opinion, anyway) version of your
code:

puts "What year should I start with?"
start_year = 1800 # gets.chomp.to_i

puts "What year should I end with?"
end_year = 1900 # gets.chomp.to_i

years = (start_year...end_year)

years.each do |year|
  if year % 4 == 0
    if year % 100 == 0
      puts "#{year} is not a leap year." if year % 400 == 0
    else
      puts "#{year} is a leap year."
    end
  else
    puts "#{year} is not a leap year."
  end
end

As a naive way of finding bugs like this, you can insert lines to print
what's going on inside your iteration. I've highlighted the debug lines with
comments, to point out the additions.

years.each do |year|
  puts "Working on #{year}"         #debug
  if year % 4 == 0
    puts "Divisible by 4"           #debug
    if year % 100 == 0
      puts "Divisible by 100"       #debug
      puts "#{year} is not a leap year." if year % 400 == 0
    else
      puts "Not divisible by 100"   #debug
      puts "#{year} is a leap year."
    end
  else
    puts "Not divisible by 4"       #debug
    puts "#{year} is not a leap year."
  end
end

Checking the output of executing this will show you something is missing:

Working on 1800
Divisible by 4
Divisible by 100
Working on 1801
Not divisible by 4
1801 is not a leap year.
Working on 1802

Hopefully this is useful.


On Fri, Jan 28, 2011 at 3:26 PM, Chris R. <chris.gogreen@gmail.com> wrote:

> Could someone tell me why in the following code, when it iterates on the
> array 'arraya' it skips the first position? It is strange because
> immediatley before each is called on arraya, I call inspect and you can
> clearly see the first value is 1800, but the first value out put is
> 1801.
>
> #code start
>
> startyear = nil
> endyear = nil
> arraya = []
> currentyearis = false
> puts 'What year should I start with?'
> startyear = gets.chomp
> puts 'What year should I end with?'
> endyear = gets.chomp
>
>
> #assign years including and between start/endyear into array
>
> arraya = (startyear...endyear).to_a
>
> #iterate on array
>
> puts arraya.inspect
>
> arraya.each do |currentyear|
>  if currentyear.to_i % 4 == 0
>    if currentyear.to_i % 100 == 0
>      puts currentyear.inspect
>      puts('The Year ' + currentyear + ' is not a leap year.') if
> currentyear.to_i % 400 == 0
>    else
>      puts('The Year ' + currentyear + ' is a leap year.')
>    end
>  else
>    puts('The Year ' + currentyear + ' is not a leap year')
>  end
> end
>
> #code end
>
> --
> Posted via http://www.ruby-forum.com/.
>
>

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