title: Append Character to String in Swift
body: <p>I'm trying to append Character to String using "+=", but It doesn't really work.
  Once I tried with append method, it works. I just wonder why it is.
  The compiler says "string is not identical to Unit8".</p>
  
  <pre><code>let puzzleInput = "great minds think alike"
  var puzzleOutput = " "
  for character in puzzleInput {
  
      switch character {
          case "a", "e", "i", "o", "u", " ":
          continue
  
      default:
          // error : doesn't work
          puzzleOutput += character
          //puzzleOutput.append(character)
      }
  }
  println(puzzleOutput)
  </code></pre>