title: How to add a character at a particular index in string in Swift
body: <p>I have a string like this in Swift:</p>
  
  <pre><code>var stringts:String = "3022513240"
  </code></pre>
  
  <p>If I want to change it to string to something like this: <code>"(302)-251-3240"</code>, I want to add the partheses at index 0, how do I do it?</p>
  
  <p>In Objective-C, it is done this way:</p>
  
  <pre><code> NSMutableString *stringts = "3022513240";
   [stringts insertString:@"(" atIndex:0];
  </code></pre>
  
  <p>How to do it in Swift?</p>