     @IBOutlet weak var display: UILabel!
 
     var userIsInTheMiddleOfTypingANumber = false
+    var userHasEnteredADot = false
     //var operands = Array<Double>()
     var operandStack = [Double]()
     var displayValue: Double {

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

    
    @IBAction func appendDigit(sender: UIButton) {
        let digit = sender.currentTitle!

        if digit  == "." && userHasEnteredADot == true {
            return
        }        
        if digit  == "." && userHasEnteredADot == false {
            userHasEnteredADot = true
        }
        
        if userIsInTheMiddleOfTypingANumber {
            display.text = display.text! + digit
