title: How do I subtract two numbers using Swift?
body: <p>I am trying to subtract to numbers that are generated randomly. I am having some problems with the code. Here is the code I have as of now:</p>
  
  <pre><code>@IBAction func subtractionButton(sender: UIButton){
      operationLabel.text = "-"
      var total == ("\(randomNumber)" - "\(secondRandomNumber)")
  }
  </code></pre>
  
  <p>The error is: 'UInt8.Type' does not have a member
  named 'covertStringInterpolationSegment'. It is on the var total line.</p>
  
  <p>I am pretty new to Swift so I may be missing something very obvious.</p>
  
  <p>Thanks in advance</p>