     
     @IBAction func enter() {
         userIsInTheMiddleOfTypingANumber = false
+        userHasEnteredADot = false
         operandStack.append(displayValue)
         println(operandStack)
     }

    
    @IBAction func appendDigit(sender: UIButton) {
        let digit = sender.currentTitle!
        
        if userIsInTheMiddleOfTypingANumber {
            display.text = display.text! + digit

    @IBOutlet weak var display: UILabel!

    var userIsInTheMiddleOfTypingANumber = false
    var userHasEnteredADot = false
    //var operands = Array<Double>()
    var operandStack = [Double]()
    var displayValue: Double {
