A quick and simple sketch app

Just to give us something to type our experiments into, we will create an extremely simplistic app, one that will present a window into which the user can type a rate of sales tax and a pre-tax price, and will present the resulting price inclusive of sales tax.

It shall be called Sales Tax Calc. I know, it's not a brilliant name.

Create a new Xcode project called SalesTaxCalc, setting it to use Storyboards.

Drag four labels and two standard text fields onto the default View Controller's View object:

The two text fields and the label in the right-hand column will need to be connected to these outlets in the ViewController.swift file:

@IBOutlet weak var rateTextField: NSTextField! 
@IBOutlet weak var preTaxTextField: NSTextField! 
@IBOutlet weak var resultLabel: NSTextField! 

The two text fields need to be connected to these two IBAction methods:

@IBAction func rateDidChange(_ sender: AnyObject){ 
} 
@IBAction func preTaxDidChange(_ sender: AnyObject){ 
} 

The whole code for the ViewController.swift file should look as follows:

import Cocoa 
class ViewController: NSViewController 
{ 
    @IBOutlet weak var rateTextField: NSTextField! 
    @IBOutlet weak var preTaxTextField: NSTextField! 
    @IBOutlet weak var resultLabel: NSTextField! 

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

    override var representedObject: Any? { 
        didSet { 
        } 
    } 

    @IBAction func rateDidChange(_ sender: AnyObject) 
    { 
        calculateFullPrice() 
    } 

    @IBAction func preTaxDidChange(_ sender: AnyObject) 
    { 
        calculateFullPrice() 
    } 

    func calculateFullPrice() 
    { 
        let currencyString = "$" 
        let rate = rateTextField.doubleValue / 100.0 + 1.0 
        let fullPrice = preTaxTextField.doubleValue * rate 
        resultLabel.stringValue = currencyString  
       + String(format: "%.2f", fullPrice) 
    } 
} 

Hit Run to test that the app builds and runs without problems.