title: Finding extension of an URL
body: <p>i have a string named url  i.e</p>
  
  <pre><code>NSString *url = @"http://sound17.mp3pk.com/indian/barfi/%5BSongs.PK%5D%20
                    Barfi%20-%2001%20-%20Barfi!.mp3";
  </code></pre>
  
  <p>Now I want that It should search from last upto the .(dot)</p>
  
  <p>i.e it should search 
   <code>mp3</code> in string as it is coming after .(dot) and want to store that <code>mp3</code> in the temporary variable.
  how can i use <code>lastindex(".")</code> or something else to store in temporary variable.</p>