Mortgage Calculator Swift - swift

Question

I am a beginner with Xcode and Swift. Below is my formula for the mortgage calculator. It is working correct in Playground but when I transfer it to the ViewController tab that is when Xcode is giving me a bunch of errors. Can someone please help?
let r: Double = interestRate / 1200
let n: Double = years * 12
let p: Double = pow(1 + r, n)
let monthPay = loan * r * p / (p - 1)
print(monthPay)
So in my View Controller
valueA is Loan Amount
valueB is Number of Payments
valueC is Interest Rate
underneath that you will have a calculate button that will print the results underneath in a label currently named results. It may be that when i rename everything to the values is when the issues occur.
ViewController Code
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var valueA: UITextField!
#IBOutlet weak var valueB: UITextField!
#IBOutlet weak var valueC: UITextField!
#IBOutlet weak var results: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func button(_ sender: Any) {
let a = Int(valueA.text!)
let b = Int(valueB.text!)
let c = Int(valueC.text!)
let answer = a! * c! * pow(1 + c!, b!) / (pow(1 + c!, b!))
results.text = "$\(answer)"
}
}

Answer 1

Your issue is that you are converting your textfield values to integers and trying to multiply them by the result of pow's method which returns a Double. Note that if the user enters an invalid value your app will crash if you force unwrap the result. Yo can use nil coalescing operator ?? to provide a default value .zero in case of failure. Try like this:
class ViewController: UIViewController {
#IBOutlet weak var valueA: UITextField! // loan amount
#IBOutlet weak var valueB: UITextField! // Number of Payments
#IBOutlet weak var valueC: UITextField! // Interest Rate
#IBOutlet weak var results: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func button(_ sender: Any) {
let loanAmount = Double(valueA.text!) ?? .zero
let numberOfPayments = Double(valueB.text!) ?? .zero
let interestRate = Double(valueC.text!) ?? .zero
let rate = interestRate / 100 / 12
let answer = loanAmount * rate / (1 - pow(1 + rate, -numberOfPayments))
results.text = Formatter.currency.string(for: answer)
}
}
extension Formatter {
static let currency: NumberFormatter = {
let formatter = NumberFormatter()
formatter.locale = .init(identifier: "en_US_POSIX")
formatter.numberStyle = .currency
return formatter
}()
}