Calculator controller before MVC. - Swift

calcBeforeMvc.swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var display: UILabel!
    
    var userIsInTheMiddleOfTypingANumber: Bool = false
    
    @IBAction func appendDigit(sender: UIButton) {
        
        // Get current value of button pressed
        let digit = sender.currentTitle!
        
        if userIsInTheMiddleOfTypingANumber {
            display.text = display.text! + digit
        }
        else{
            display.text = digit
            userIsInTheMiddleOfTypingANumber = true
        }
    }
    
    // plus minus x divide function.
    @IBAction func operate(sender: UIButton) {
        // Set the symbol pressed
        let operation = sender.currentTitle!
        //when symbol pressed check for case
        if userIsInTheMiddleOfTypingANumber{
            enter()
        }
        switch operation{
            case "×": performOperation() { $0 * $1 }
            case "÷": performOperation() { $1 / $0 }
            case "+": performOperation() { $0 + $1 }
            case "-": performOperation() { $1 - $0 }
            case "√": performOperation() { sqrt($0) }
            default : break
        }
    }
    
    private func performOperation(operation: (Double, Double) -> Double){
        if operandStack.count >= 2 {
            displayValue = operation(operandStack.removeLast(), operandStack.removeLast())
            enter()
        }
    }
    private func performOperation(operation: (Double) -> Double){
        if operandStack.count >= 1 {
            displayValue = operation(operandStack.removeLast())
            enter()
        }
    }
    
    //var is array = init a empty array. this is an array of doubles.
    var operandStack = Array<Double>()
    
    @IBAction func enter() {
        userIsInTheMiddleOfTypingANumber = false
        operandStack.append(displayValue)
        println("operandStack = \(operandStack)")
    }
    
    var displayValue: Double {
        get {
            return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
        }
        set{
            display.text = "\(newValue)"
            userIsInTheMiddleOfTypingANumber = false
        }
    }
}