incorrect contact.rb code

require "./phone_number"
require "./address"

class Contact
  attr_writer :first_name, :middle_name, :last_name
  attr_reader :phone_numbers, :address

  def initialize
    @phone_numbers = []
    @address = []
  end

  def add_phone_number(kind, number)
    phone_number = PhoneNumber.new
    phone_number.kind = kind
    phone_number.number = kind
    phone_numbers.push(phone_number)
  end

  def add_address(kind, street_1, street_2, city, state, postal_code)
    address = Address.new
    address.kind = kind
    address.street_1 = street_1 
    address.street_2 = street_2
    address.city = city
    address.state = state
    address.postal_code = postal_code
    addresses.push(address) 
  end

  def first_name
    @first_name
  end

  def middle_name
    @middle_name
  end

  def last_name
    @last_name
  end

  def first_last
    first_name + " " + last_name
  end

  def last_first
   last_first = last_name
    last_first += ", "
    last_first += first_name
    if !@middle_name.nil?
      last_first += " "
      last_first += middle_name.slice(0, 1)
      last_first += "."
    end
    last_first
  end

  def full_name
    full_name = first_name
    if !@middle_name.nil?
      full_name += " "
      full_name += middle_name
    end
    full_name += " "
    full_name += last_name
    full_name 
  end

  def to_s(format = "full_name")
    case format
     when 'full_name'
      full_name
     when 'last_first'
      last_first   
      when 'first'
        first_name
      when 'last'
        last_name
      else 
        first_last
    end
  end

  def print_phone_numbers
    puts "Phone Numbers"
    phone_numbers.each { |phone_number| puts phone_number }
   end

  def print_addresses
     puts "Addresses"
     addresses.each { |address| puts.address.to_s('short') }
  end  
end