Calculator in Swift

Question

I have some logic problem about this calculator. When I push the "=" after first time executive it'll execute twice with same operand.

For example:

"1"+"2"="3"

"3" + "2", then output -> "5" before I press another operands.

Here is the source code:

https://drive.google.com/file/d/0B1a-AefbM9rOUTdyVmdJOWhNNnc/view?usp=sharing

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var display: UILabel!
    
    var MiddleTyping = false
    
    @IBAction func appandDigit(sender: UIButton) {
        let digit = sender.currentTitle!
        if MiddleTyping{
            display.text = display.text! + digit
        }else{
            display.text = digit
            MiddleTyping = true
        }
    }
    
    
    
    var operandStack = [Double]()
    var binaryoperation = [String]();
    var firstTimeInputNumber = true
    
    var displayValue: Double{
        get{
            return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
        }
        set{
            display.text = "\(newValue)"
            MiddleTyping = false
        }
    }
    @IBAction func Operate(sender: UIButton) {
        MiddleTyping = false
        var equalOperand = ""
        var Operation = ""
        if sender.currentTitle == "="{
             equalOperand = binaryoperation.last ?? ""
        }else{
              Operation = sender.currentTitle!
        }
        if operandStack.count == 1 && binaryoperation.count != 0{
            operandStack.append(displayValue)
        }
        if operandStack.count == 2{
            if equalOperand == binaryoperation.last ?? "" {
                switch equalOperand{
                case "×":
                    displayValue = operandStack[0] * operandStack[1]
                    operandStack[0] = displayValue
                case "÷":
                    displayValue = operandStack[0] / operandStack[1]
                    operandStack[0] = displayValue
                case "+":
                    displayValue = operandStack[0] + operandStack[1]
                    operandStack[0] = displayValue
                case "−":
                    displayValue = operandStack[0] - operandStack[1]
                    operandStack[0] = displayValue
                default: break
                }
            }else{
                let Operation = binaryoperation.last ?? "";
                switch Operation {
                case "×":
                    displayValue = operandStack[0] * operandStack[1]
                    operandStack[0] = displayValue
                    operandStack.removeLast()
                case "÷":
                    displayValue = operandStack[0] / operandStack[1]
                    operandStack[0] = displayValue
                    operandStack.removeLast()
                case "+":
                    displayValue = operandStack[0] + operandStack[1]
                    operandStack[0] = displayValue
                    operandStack.removeLast()
                case "−":
                    displayValue = operandStack[0] - operandStack[1]
                    operandStack[0] = displayValue
                    operandStack.removeLast()
                default: break
                }
            }
        }
        if displayValue != 0 {
            if firstTimeInputNumber{
                operandStack.append(displayValue)
            }
            firstTimeInputNumber = false
        }
        if Operation != ""{
            binaryoperation.append(Operation)
        }
        println("push op \(operandStack)")
        println("push op \(binaryoperation)")
    }
    @IBAction func ClearButton() {
        operandStack.removeAll()
        binaryoperation.removeAll()
        display.text = "0"
        firstTimeInputNumber = true
        MiddleTyping = false
        
    }
}

Answer 1

All I can image is the conditionbinaryoperation.count != 0 may be binaryoperation.count == 1, that is, you don't remove the operator when you perform calculate