in_words_recursive.rb

module InWords
  def in_words()
  
    if self == 0
      return "zero"
    end
    
    lvl_array = %w{ not_called thousand million billion trillion }
    max_lvl = (self.to_s.length - 1) / 3
    n = self
    ar = []

    0.upto(max_lvl) do |lvl|
      hundreds = n % 1000
      ar.unshift(lvl_array[lvl]) unless hundreds == 0 || lvl == 0
      ar.unshift(hundreds.in_words_hundreds) unless hundreds == 0
      n /= 1000
    end
    
    ar.join(" ")
  end
  
  def in_words_hundreds()
    ones_array = %w{ not_called one two three four five six seven eight nine ten}
    tens_array = %w{ not_called not_called twenty thirty forty fifty sixty seventy eighty ninety}
    teens_array = [ "" ] + %w{ one two three four five six seven eight nine ten eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen}

    hundreds = self / 100
    two_digit = self % 100

    if two_digit < 20
      tens_word = teens_array[two_digit]
    else
      tens = two_digit / 10
      ones = two_digit % 10

      tens_word = tens_array[tens]
      tens_word << " " + ones_array[ones] unless ones == 0
    end

    if hundreds == 0
      tens_word
    else
      hundreds_word = ones_array[hundreds] + " hundred"
      hundreds_word << " " + tens_word unless two_digit == 0
      hundreds_word
    end
  end
end

class Fixnum
    include InWords
end