Swift error when I press button more times than there are pizzas in my array list - swift

Question

So I just started programming and I am now getting this error.
It occurs every time I press the button more times than there are Pizzas in the list.
Full error code: Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0):
Here`s my code so far:
import UIKit
var pizzaNumber = 0
var pizzaNames = ["Skinke Pizza", "Salat Pizza", "Pepperoni Pizza"]
let priser = [65,70,65]
var totalProdukt = pizzaNames.count
class ViewController: UIViewController {
#IBOutlet weak var produktNavn: UILabel!
#IBAction func rightButton(_ sender: UIButton) {
pizzaNumber+=1
showPizza()
}
#IBAction func leftButton(_ sender: UIButton) {
pizzaNumber-=1
if pizzaNumber < 0 {
pizzaNumber = 0
}
showPizza()
}
func showPizza() {
if pizzaNumber > totalProdukt {
pizzaNumber = pizzaNames.count
} else {
self.produktNavn.text = pizzaNames[pizzaNumber]
}
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}

Answer 1

You should make sure that pizzaNumber-1 can never be bigger than the number of elements in your array to ensure that you are never trying to access an index that doesn't exist. This can be easily done by changing totalProdukt to be a computed variable. This way, the value of the variable will always be updated when you are trying to access it.
var totalProdukt: Int {
return pizzaNames.count
}
Also bear in mind that array indexing starts at 0, so you need
if pizzaNumber >= totalProdukt {
pizzaNumber = pizzaNames.count-1
} else {
self.produktNavn.text = pizzaNames[pizzaNumber]
}
Bear in mind that with your current code, there's no need for storing the count of the array in a separate variable, since you are only using it at one place in code.
Moreover, the cleanest solution is to check the value before actually increasing it rather than when using it, this way in showPizzas you don't need to do any checks, just update the label:
class ViewController: UIViewController {
#IBOutlet weak var produktNavn: UILabel!
#IBAction func rightButton(_ sender: UIButton) {
if pizzaNumber < pizzas.count-1 {
pizzaNumber+=1
}
showPizza()
}
#IBAction func leftButton(_ sender: UIButton) {
if pizzaNumber > 0 {
pizzaNumber-=1
}
showPizza()
}
func showPizza() {
self.produktNavn.text = pizzaNames[pizzaNumber]
}
}

Answer 2

Here's how to fix your error
func showPizza() {
if pizzaNumber >= totalProdukt { // << Added '=' since pizzaNames[pizzaNames.count] is out of bounds
pizzaNumber = pizzaNames.count - 1
} else {
self.produktNavn.text = pizzaNames[pizzaNumber]
}
}