Get an english ordinal string ('1st', '2nd', '3rd', etc) from an integer

english_ordinal.rb

  def english_ordinal n
    str = n.to_s
    str +
    case str
    when /11$/, /12$/, /13$/
      'th'
    when /1$/
      'st'
    when /2$/
      'nd'
    when /3$/
      'rd'
    else
      'th'
    end
  end