SWIFT: Adding Double and a String to then display on a label : I am trying to add up a value that is entered in the text field with a value specified as a double and then returning the value on a label. I would appreciate, if someone could assist. I am a complete beginner so probably something very obvious :( . The code that I have is : 

    @IBOutlet weak var enterField: UITextField!
    
    var weekOneTotal:Double = 0
    
     @IBAction func addButton(_ sender: Any) {
            addCorrectValue()
            
        }
    
    func addCorrectValue () {
            guard let addAmount = convertAmount(input: enterField.text!) else {
                print("Invalid amount")
                return
            }
    
          let newValue = weekOneTotal += addAmount
            
            secondScreen.weekOneAmountLabel.text = String(newValue)
    
    }
    
      func convertAmount (input:String) -> Double? {
            
            let numberFormatter = NumberFormatter ()
            numberFormatter.numberStyle = .decimal
            
            return numberFormatter.number(from: input)?.doubleValue
        }
        



