title: Getting differences between two NSStrings
body: <p>I've got two <code>NSString</code>s and I want to get the differences between them.</p>
  
  <p>Let me make an example:</p>
  
  <pre><code>NSString *pippo = @"pippo";
  NSString *pippone = @"pippone";
  </code></pre>
  
  <p>I would like to get the different characters in the two instances. How can I do that?</p>