Can't update var value with text field value. Swift - swift

Question

I am creating an app for a project that determines whether or not a year is a leap year or not.
The overall logic itself is very simple, however I am trying to make it so when the button is pressed, it will take the value within the text field and then update var year with that value.
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var guessLabel: UILabel!
#IBOutlet weak var guessTextField: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
func logic() {
// var year = guessTextField This is where the issue is.
var value1 = (year % 4)
var value2 = (year % 100)
var value3 = (year % 400)
var criteria: Bool!
print (value1)
print (value2)
criteria = false
func yearChecker() {
if value1 == 0 {
criteria = true
}
if value2 != 0, value1 == 0 {
criteria = true
}
if value3 == 0, value1 == 0 {
criteria = true
}
if criteria == true {
leapYearAlert()
}
if criteria == false {
showBoundsAlert()
}
}
}
#IBAction func submitButton(_ sender: UIButton) {
var year = guessTextField.text
logic()
}
func showBoundsAlert() {
let alert = UIAlertController(title: "Sorry, The Year You Chose is Not Special", message: "You're Year is Not a Leap Year:(", preferredStyle: .alert)
let action = UIAlertAction(title: "Okay", style: .default, handler: nil)
alert.addAction(action)
self.present(alert, animated: true, completion: nil)
}
func leapYearAlert() {
let alert = UIAlertController( title: "Your Year is Special!", message: "The Year You Chose is in Fact a Leap Year!", preferredStyle: .alert)
let action = UIAlertAction(title: "Check For Another Year?", style: .default, handler: nil)
alert.addAction(action)
self.present(alert, animated: true, completion: nil)
}
}

Answer 1

Cast year as Int because guessTextField.text return String.
#IBAction func submitButton(_ sender: UIButton) {
logic()
}
Change value1, value2, value3 from var to let as they don't change.
func logic() {
let year: Int = Int(guessTextField.text ?? "0")!
let value1: Int = (year % 4)
let value2: Int = (year % 100)
let value3: Int = (year % 400)
var criteria: Bool = false
print (value1)
print (value2)
if value1 == 0 {
criteria = true
}
if value2 != 0, value1 == 0 {
criteria = true
}
if value3 == 0, value1 == 0 {
criteria = true
}
if criteria == true {
leapYearAlert()
} else {
showBoundsAlert()
}
}