A nil class when trying to initialize a deck of cards - ruby

Question

The following code is resulting in nil and I can't figure out why. Is there something wrong with my initialization?
class Card
VALUES = %w(2 3 4 5 6 7 8 9 10 J Q K A)
SUITS = %w(S H D C)
def initialize(suit, value)
#suit = suit
#value = value
end
end
class Deck
attr_accessor :cards
def initialize
#cards = []
Card::SUITS.each do |suit|
Card::VALUES.each do |value|
#cards << Card.new(suit, value)
end
end
end
end
Deck.new
p #cards

Answer 1

#cards is not known outside the object. Outside the class Deck it is a instance variable of the top-level scope in Ruby.
You have to use the accessor method to get the content:
class Card
VALUES = %w(2 3 4 5 6 7 8 9 10 J Q K A)
SUITS = %w(S H D C)
def initialize(suit, value)
#suit = suit
#value = value
end
end
class Deck
attr_accessor :cards
def initialize
#cards = []
Card::SUITS.each do |suit|
Card::VALUES.each do |value|
#cards << Card.new(suit, value)
end
end
end
end
deck = Deck.new #<--- Store object in a variable
p deck.cards #<--- Use accessor

Answer 2

or just:
my_deck = Deck.new
p my_deck.cards

Answer 3

In short, instance variables can only be seen by other methods from within the same class. I believe what you're trying to do is:
new_deck = Deck.new
p new_deck.cards
Calling the cards method on new_deck returns #cards.

Answer 4

You create a new object Deck.new, but you don't print the value of its cards - you print a #cards instance variable which in this context is nil.
You probably wanted something like p Deck.new.cards.

Answer 5

Currently your output for #cards array is difficult to read and contains object info. I thought I'd offer an alternative I've just conjoured up, hope it helps:
class Deck
attr_writer :suits, :values
attr_accessor :deck
def initialize
suits
values
generate_deck
shuffle
end
def generate_deck
#deck = []
#suits.each do |suit|
#values.each { |value| #deck << [suit, value] }
end
end
def suits
#suits = ['Clubs', 'Diamonds', 'Hearts', 'Spades' ]
end
def values
#values = ('2'..'10').to_a + ['J','Q','K','A']
end
#just in case you want to shuffle your deck
def shuffle
#deck.shuffle!
end
end
require 'pp' #this makes the output prettier
new_deck = Deck.new
pp new_deck.deck #calls your current deck so you can see it
Output example:
$ ruby yourfilename.rb
[["Hearts", "K"],
["Spades", "5"],
["Clubs", "7"],
#code omitted... (the rest of your cards would be here)
["Clubs", "K"],
["Hearts", "5"],
["Diamonds", "J"],
["Hearts", "7"]]