     //MARK: UIVIew Delegate
     
     override func viewDidLoad() {
-        
         // round the corners of the calculator on iPhone X
-        if iPhoneModel == .iPhoneX || iPhoneModel == .simulator(.iPhoneX){
+        if iPhoneModel == .iPhoneX || iPhoneModel == .simulator(.iPhoneX) {
             cornerView.layer.cornerRadius = 35
             cornerView.layer.masksToBounds = true
         } 

    }
    
    @IBAction func performOperation(_ sender: UIButton) {
        
        if userIsInTheMiddleOfTyping {
            brain.setOperand(displayValue)
            userIsInTheMiddleOfTyping = false

    //MARK: IBAction(s)
    
    @IBAction func touchDigit(_ sender: UIButton) {
        guard let digit = sender.currentTitle else { return }
        
        if userIsInTheMiddleOfTyping {
            guard let textCurrentlyInDisplay = display.text else { return }
            
            if digit == "." && (textCurrentlyInDisplay.range(of: ".") != nil) {
                return
