ninety_nine_bottles_of_beer.rb

def english_number number

  return 'Please enter a number that isn\'t negative.' if number < 0
  return 'zero' if number == 0

  # No more special cases! No more returns!
  num_string = '' # This is the string we will return.
  ones_place = %w(one two three four five six seven eight nine)
  tens_place = %w(ten twenty thirty forty fifty sixty seventy eighty ninety)
  teenagers  = %w(eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen)

  # "left" is how much of the number
  #         we still have left to write out.
  #  "write" is the part we are
  #          writing out right now.
  #  write and left...get it?  :)

  left = number
  write = left/1000000000 # How many billions left?
  left = left - write*1000000000 # Subtract off those billions.

  if write > 0
    # Now here's the recursion:
    billions = english_number write
    num_string = num_string + billions + ' billion'
    if left > 0
      num_string = num_string + ' '
    end
  end

  write = left/1000000 # How many millions left?
  left = left - write*1000000 # Subtract off those millions.

  if write > 0
    # Now here's the recursion:
    millions = english_number write
    num_string = num_string + millions + ' million'
    if left > 0
      num_string = num_string + ' '
    end
  end

  write = left/1000 # How many thousands left?
  left = left - write*1000 # Subtract off those thousands.

  if write > 0
    # Now here's the recursion:
    thousands = english_number write
    num_string = num_string + thousands + ' thousand'
    if left > 0
      num_string = num_string + ' '
    end
  end

  write = left/100 # How many hundreds left?
  left = left - write*100 # Subtract off those hundreds.

  if write > 0
    # Now here's the recursion:
    hundreds = english_number write
    num_string = num_string + hundreds + ' hundred'
    if left > 0
      #  So we don't write 'two hundredfifty-one'...
      num_string = num_string + ' '
    end
  end

  write = left/10 # How many tens left?
  left = left - write*10 # Subtract off those tens.

  if write > 0
    if ((write == 1) and (left > 0))
      #  Since we can't write "tenty-two" instead of
      #  "twelve", we have to make a special exception
      #  for these.
      num_string = num_string + teenagers[left-1]
      # The "-1" is because teenagers[3] is
      # 'fourteen', not 'thirteen'.
      # Since we took care of the digit in the
      # ones place already, we have nothing left to write.
      left = 0
    else
      num_string = num_string + tens_place[write-1]
      #  The "-1" is because tens_place[3] is
      # 'forty', not 'thirty'.
    end
    if left > 0
      # So we don't write 'sixtyfour'...
      num_string = num_string + '-'
    end
  end

  write = left # How many ones left to write out?
  left = 0 # Subtract off those ones.

  if write > 0
    num_string = num_string + ones_place[write-1]
    # The "-1" is because ones_place[3] is
    # 'four', not 'three'.
  end
  #  Now we just return "num_string"...

  num_string
end

max_number = gets.chomp.to_i
(1..max_number).reverse_each do |current_number|
  number = english_number current_number
  number_minus_one = english_number current_number - 1
  puts "#{number} bottles of beer on the wall, #{number} bottles of beer."
  puts "Take one down and pass it around, #{number == 'one' ? 'No more' : (number_minus_one) } bottles of beer on the wall."
  puts ''
end
max_number_english = english_number max_number
puts 'No more bottles of beer on the wall, no more bottles of beer.'
puts "Go to the store and buy some more, #{max_number_english} bottles of beer on the wall."