Printing variables

Question

My problem is probably quite easy, but I couldn't find an answer anywhere.

When create a class, for example:

class Book
  @author = "blabla"
  @title = "blabla"
  @number_of_pages"

I want to create a method to print out my variables. And here I'm getting a problem when I try:

def Print
  puts @author, @title, @number_of_pages
end

I am getting nothing.

When I try:

def Print
  puts "@author, @title, @number_of_pages"
end

I get straight: "@author, @title, @number_of_pages"

How can I make the Print method print out the variables' values?

Answer 1

You should move your variable initializations to initialize:

class Book
  def initialize
    @author = "blabla"
    @title = "blabla"
    @number_of_pages = 42 # You had a typo here...
  end
end

The way you have it in your question, the variables are class instance variables (which you can Google if you're curious about, but it's not really relevant here).

Initialized as (normal) instance variables, your first version of Print() works if you're just looking to dump the state -- it prints each parameter on its own line.

To make your second version of Print() work, you need to wrap your variables in #{} to get them interpolated:

def print # It's better not to capitalize your method names
  puts "#{@author}, #{@title}, #{@number_of_pages}"
end

Answer 2

In addition to the allready exellent answer of Darshan, here is the way you would do it optimally

class Book

  attr_accessor :author, :title, :number_of_pages 
  #so that you can easily read and change the values afterward

  def initialize author, title, number_of_pages = nil 
    #so that you don't really need to provide the number of pages
    @author = author
    @title = title
    @number_of_pages = number_of_pages
  end

  def print
    puts "#{@author}, #{@title}, #{@number_of_pages}" 
  end 
end 

my_book = Book.new("blabla", "blabla", 42)
my_book.title = "this is a better title"
my_book.print

#=>blabla, this is a better title, 42