override func viewDidLoad() {
    super.viewDidLoad()
    let checkForFirstTimeLaunch = UserDefaults.standard.string(forKey: "Flag")

    if checkForFirstTimeLaunch == false {
        print("First time launch")

        //if user launches app for the first time, it will go here
        let PageViewController = self.storyboard?.instantiateViewController(withIdentifier: "PageViewController") as! PageViewController

        self.present(PageViewController, animated: true)
    } else {
        //otherwise, it will go here
        let HomeViewController = self.storyboard?.instantiateViewController(withIdentifier: "HomeViewController") as! HomeViewController

        self.present(HomeViewController, animated: true)
    }
}

if checkForFirstTimeLaunch == nil {
    //First time launch
} else {
    //Not first time launch
}

let firstTimeLaunch = UserDefaults.standard.bool(forKey: "Flag")

if firstTimeLaunch == false {
    //first time launch
} else {
    //not first time launch
}