Number formatting with columns. You should have better implementation. :-P

integer_ext.rb

class Integer
  def to_cs(numcol = 3)
    unit = 10 ** numcol
    reps = '\d' * numcol
    neg = false
    str = self.to_s
    if self <= -unit
      neg = true
      str = (-self).to_s
    elsif self < unit
      return str
    end
    str = str.reverse.gsub(/(#{reps})/, '\1,').gsub(/,$/, '').reverse
    str = '-' + str if neg
    str
  end
end