電卓を作ってみたのですが...

swift初心者です。
今回、swiftで簡単な電卓を作ってみたのですが、AppDelegate.swiftでエラーが起きてしまいアプリが中断されてしまいます。
エラー内容はclass AppDelegate: UIResponder, UIApplicationDelegate の行で以下のようなエラー文でした。

Thread 1: signal SIGABRD

そして、下にはViewController.swiftのソースを載せます。```lang-swift
import UIKit

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    myButton0.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton1.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton2.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton3.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton4.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton5.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton6.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton7.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton8.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButton9.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    
    myButtonPlus.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButtonMinus.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButtonMulti.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButtonDivision.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
    myButtonEqual.addTarget(self, action: "buttonClicked", forControlEvents: .TouchUpInside)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBOutlet weak var myLabel: UILabel!;

// 数字を表すプロパティ
@IBOutlet weak var myButton0: UIButton!;
@IBOutlet weak var myButton1: UIButton!;
@IBOutlet weak var myButton2: UIButton!;
@IBOutlet weak var myButton3: UIButton!;
@IBOutlet weak var myButton4: UIButton!;
@IBOutlet weak var myButton5: UIButton!;
@IBOutlet weak var myButton6: UIButton!;
@IBOutlet weak var myButton7: UIButton!;
@IBOutlet weak var myButton8: UIButton!;
@IBOutlet weak var myButton9: UIButton!;

@IBOutlet weak var myButtonPlus: UIButton!;//足し算のプロパティ
@IBOutlet weak var myButtonMinus: UIButton!;//引き算のプロパティ
@IBOutlet weak var myButtonMulti: UIButton!;//掛け算のプロパティ
@IBOutlet weak var myButtonDivision: UIButton!;//割り算のプロパティ

@IBOutlet weak var myButtonEqual: UIButton!;

func buttonClicked(sender: UIButton){
    switch sender {
    case myButtonPlus,myButtonMinus,myButtonMulti,myButtonDivision:
        command = sender.titleLabel!.text!;
        inputR = true;//右辺の入力に移る
        
    case myButtonEqual:
        //ボタンがタップされた
        if inputR {
            var result: Int?;
                
            switch command {
            case "+":
                result = left.toInt()! + right.toInt()!;
            case "-":
                result = left.toInt()! - right.toInt()!;
            case "*":
                result = left.toInt()! * right.toInt()!;
            case "/":
                result = left.toInt()! / right.toInt()!;
                    
            default :
                result = 0;
            }
            myLabel.text = "\(result)";//結果の表示
            //次の入力のためのデータの初期化
            left = "";
            right = "";
            inputR = false;
        }
        
    default :
        //ボタン0-9がタップされた時
        if inputR {
            //右辺入力時の動作
            right = right + sender.titleLabel!.text!;
            myLabel.text = right;
        } else {
            //左辺入力中なら
            left = left + sender.titleLabel!.text!;
            myLabel.text = left;
            
        }
        
    }
    
}

var right: String = "";//計算の右辺となる文字列
var left: String = "";//計算の左辺となる文字列
var inputR: Bool = false;//右辺を入力中かどうか
var command: String = "";//計算に使用するコマンド

}