Why is my app not running?

    @IBOutlet weak var funFactLabel: UILabel!

let factBook = FactBook()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    funFactLabel.text = factBook.randomFact()
}

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


@IBAction func showFunFact() {
    funFactLabel.text = factBook.randomFact()
}

let factsArray = [
    "Ants strech when they wake up in the morning.",
    "Ostriches can run faster than horses.",
    "Olympic gold metals are actually made of mostly silver.",
    "You are born with 300 bones; by the time you are an adult, you will have 206.",
    "It takes about 8 minutes for light from the Sun to reach Earth.",
    "Some bamboo plants can grow up to a meter in a day.",
    "Some penguins can leap 2-3 meters out of the water.",
    "The state of Florida is bigger than England.",
    "On average, it takes 66 days to form a new habit.",
    "Mammoths still walked the earth when the Great Pyramid was being build."
]

func randomFact() -> String {
    let unsignedArrayCount = UInt32(factsArray.count)
    let unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
    let randomNumber = Int(unsignedRandomNumber)

    return factsArray[randomNumber]

}