title: Ruby 'is_a?' class or module required (TypeError)
body: <p>I'm playing around with Ruby and trying create a little bank account program.  When I run this particular line of code which is running withing the create_account:</p>
  
  <pre><code>unless @response.is_a? Integer &amp;&amp; @response.to_str.length == 4
      puts "Your response must be 4 numbers in length."
      create_account
  else
      @pin = @response
      puts "Your pin has been set."
  end
  </code></pre>
  
  <p>I get this response: </p>
  
  <pre><code>bank_account.rb:24:in 'is_a?':class or module required (TypeError)
      from bank_account.rb:24:in 'create_account'
      from bank_account.rb:47:in '&lt;main&gt;'
  </code></pre>
  
  <p>I can't exactly figure out what's going on, but I'm including the rest of my code.  It's incomplete, obviously because I'm stuck on this part.  I go through a while loop and enter 'Create Account' to start the create_account method.  My goal is to run the conditional and require the user to type a 4 digit integer, like any ole pin number.  If it is not an integer nor 4 digits in length, I call the create_account method to get them to start over.</p>
  
  <p>I'm running ruby 2.0.0 if that information is necessary, but I wager it is likely more to do with my code.  Stackoverflow is new to me, so I apologize if this question has been asked.  I tried to do my homework as is advised before asking a question, but I'm still stumped.  Any help is appreciated.</p>