title: How to use StringByAppendingFormat in XCode6
body: <p>Code:</p>
  
  <pre><code>var postString: NSString = NSString .stringByAppendingFormat("userName=\(userName) &amp; password = \(Password)")
  </code></pre>
  
  <p>Why I am getting error as:</p>
  
  <pre><code>(NSString, CVarArgType...) -&gt; NSString' is not convertible to NSString.
  </code></pre>