title: Reversing the order of a string value
body: <p>I have the following function which reverses a string value's display order. 
  I'm new to Swift and I'm trying to understand it's logic. What is going on with the '!pleh' value that it turns into 'Help!' ? 
  Thanks</p>
  
  <pre><code>func reverse(_ s: String) -&gt; String {
   var str = ""
   for character in s.characters {
      str = "\(character)" + str
   }
   return str
  }
  print (reverse("!pleH"))
  </code></pre>