numbers in words

in_words.rb

class Integer
  def in_words
    up_to_twenty = {     0 => "\b",
                         1 => "one",
                         2 => "two",
                         3 => "three",
                         4 => "four",
                         5 => "five",
                         6 => "six",
                         7 => "seven",
                         8 => "eight",
                         9 => "nine",
                         10 => "ten",
                         11 => "eleven",
                         12 => "twelve",
                         13 => "thirteen",
                         14 => "fourteen",
                         15 => "fifteen",
                         16 => "sixteen",
                         17 => "seventeen",
                         18 => "eighteen",
                         19 => "nineteen" }
    tens = {             20 => "twenty",
                         30 => "thirty",
                         40 => "forty",
                         50 => "fifty",
                         60 => "sixty",
                         70 => "seventy",
                         80 => "eighty",
                         90 => "ninety" }
    thousands_and_up = { 10 ** 3 => "thousand",
                         10 ** 6 => "million",
                         10 ** 9 => "billion",
                         10 ** 12 => "trillion" }
    if self < 20
      up_to_twenty[self]
    elsif self < 100
      "#{tens[self - (self % 10)]} #{(self % 10).in_words}"
    elsif self < 1_000
      "#{(self / 100).in_words} hundred #{(self % 100).in_words}"
    else
      thousands_and_up.each do |number, word|
         if (self / number) >= 1 && (self / number) < 1_000
           return "#{(self / number).in_words} #{word} #{(self % number).in_words}"
         end
       end
    end
  end
end