Move numbers from right to left of a decimal point in iOS Swift 5.3

Question

I'm trying to make my numbers (taken from custom button input) to move from right to left with two decimal places. I'm using 10 buttons (0-9) with sender tags attached to them for the buttonInput and I want the right to left decimal number to appear in the labelText label. I know you can use textfields to accomplish this, but I want to use my custom buttons.

Desired outcome: user taps 1 button, labelText changes to $0.01; user taps 2 button, labelText changes to $0.12; etc..

Xcode Version 12.1; Swift Version 5.3

Here's what I've got so far.. I'm new to Swift, so go easy on me!

@IBOutlet weak var labelText: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
}

@IBAction func numPad(_ sender: UIButton) {
    //button number
    let buttonInput = Double(sender.tag - 1)
    
    //label text to number conversion
    let labelValue = labelText.text
    let intValue = Double(labelValue!)
    
    //move number to the right of decimal
    //let addedValue = (intValue! * 0.10) + buttonInput
    let addedValue = intValue! + buttonInput
    
    let numForm = NumberFormatter()
    numForm.numberStyle = .decimal
    //numForm.currencySymbol = "$"
    numForm.minimumIntegerDigits = 0
    numForm.maximumIntegerDigits = 4
    numForm.maximumFractionDigits = 2
    numForm.minimumFractionDigits = 2
    
    labelText.text = numForm.string(for: addedValue)
}

Answer 1

All you need is to convert your button tag to Double, divide it by 100, and sum it to the current value of your label multiplied by 10:

let cents = Double(sender.tag - 1)/100
print("cents", cents)
let oldValue = (Double(labelText.text!) ?? .zero) * 10
print("oldValue", oldValue)
let newValue = oldValue + cents
print("newValue", newValue)

Note: You should never use your UI to hold values, only to display them. I would also use Decimal instead of Double to preserve its fractional digits precision:

---

var labelValue: Decimal = .zero

---

let cents = Decimal(sender.tag - 1)/100
print("cents", cents)
let newValue = labelValue * 10
print("newValue", newValue)
labelValue = newValue + cents
print("labelValue", labelValue)
let numForm = NumberFormatter()
numForm.numberStyle = .decimal
numForm.minimumIntegerDigits = 1
numForm.maximumIntegerDigits = 4
numForm.maximumFractionDigits = 2
numForm.minimumFractionDigits = 2

labelText.text = numForm.string(for: labelValue)