title: error: cannot convert value of type 'String' to expected argument type 'Character'
body: <p>I am running into this error using Swift 4. I'm attempting to get the index of an element in an array.  </p>
  
  <pre><code>if removedLetters.contains(selectedLetter!) {
      print("\(selectedLetter!) is in the word")
      print(theWordArray.index(of: "\(selectedLetter)"))
  }
  </code></pre>
  
  <p>results in <code>error: cannot convert value of type 'String' to expected argument type 'Character'</code>  <br></p>
  
  <p>I also tried creating a character variable <code>var selectedChar:Character = selectedLetter</code> but I get a conversion error: <code>error: cannot convert value of type 'String?' to specified type 'Character'</code></p>