title: Xcode, where to assign the segue identifier
body: <p>Pardon me for beginner's question.
  I know I can switch to another screen (ViewController) like this</p>
  
  <pre><code>self.performSegueWithIdentifier ("SecondViewController", sender: self)
  </code></pre>
  
  <p>but I can't seem to find where to assign my 2nd screen the id, I just find Storyboard ID, is that it? </p>
  
  <p>I've already tried, only received a crash with the following error: </p>
  
  <blockquote>
    <p>Receiver () has no segue
    with identifier 'SecondViewController'</p>
  </blockquote>
  
  <p>Any idea? thanks</p>