Seguindo orogramação @iOS: The Big Nerd Ranch Guide, 6ª Edição, tento fazer um projeto de questionário usando rapidament

O código do ViewController aqui

import UIKit

class ViewController: UIViewController {
    @IBOutlet var questionLabel: UILabel!
    @IBOutlet var answerLabel: UILabel!

    let questions: [String] = [
        "What is 7+7?",
        "What is the capital of Vermont?",
        "What is cognac made from?"
    ]
    let answers: [String] = [
        "14",
        "Montpelier",
        "Grapes"
    ]
    var currentQuestionIndex: Int = 0

    @IBAction func showNextQuestion(_ sender: UIButton) {
        currentQuestionIndex += 1
        if currentQuestionIndex == questions.count {
            currentQuestionIndex = 0
        }

        let question: String = questions[currentQuestionIndex]
        questionLabel.text = question
        answerLabel.text = "???"
    }

    @IBAction func showAnswer(_ sender: UIButton) {
        let answer: String = answers[currentQuestionIndex]
        answerLabel.text = answer
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        questionLabel.text = questions[currentQuestionIndex]
    }
}

Mas executando com texto não visual, exceto o in