Error to show the calculation error on iOS app

Question

I'm creating iOS app that respond the inputted variables.

However, there is one error message to print the result and I have no idea to fix the error.

First Error Message

        let result = x + y
        label.text = "result is \(result) "

Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value

What I tried to do

After getting the first comment, I have double checked ResultViewController.swift and the transition page was changed.

What I need is to show result is 2 instead res... How can I fix it?

ViewController.swift

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // aquire ResultViewController from segue
        let resultViewController:ResultViewController = segue.destination as! ResultViewController
        // set numbers
        resultViewController.x = 1
        resultViewController.y = 1
    }

    @IBAction func unwind(_ segue: UIStoryboardSegue) {
        // called after returning back from segue 
    }
}

ResultViewController.swift

import UIKit

class ResultViewController: UIViewController {

    @IBOutlet weak var label: UILabel!

    var x:Int = 0
    var y:Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.

        let result = x + y
        label.text = "result is \(result) "
    }
}

Answer 1

Add constraints on your label either from storyboard or programatically

 override func viewDidLoad() {
         super.viewDidLoad()

            label.translatesAutoresizingMaskIntoConstraints = false
            label.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
            label.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
            label.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
            label.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true

            let result = x + y
            label.text = "result is \(result) "
        }

or whatever constraint you want to add on your label