title: Find out the extension part of URL saved in NSString
body: <p>How to find out and save the extension of fields that i am going to save in photo album. i want know it which format.
  example: </p>
  
  <p><a href="http://www.example.com/myvideo.mp4" rel="nofollow noreferrer">http://www.example.com/myvideo.mp4</a>,
  <a href="http://www.example.com/mypicture.png" rel="nofollow noreferrer">http://www.example.com/mypicture.png</a></p>
  
  <p>I need is like  .mp4 and .png.If possible give me example code.</p>