title: Display numbers, operator signs, and sum in UILabel
body: <p>I am relatively new to Xcode. I am making a dice roller app in which six buttons representing six different dice (from d4 to d20) can be pressed, and the roll for the most recently tapped dice is displayed in one UILabel. There is also a Clear button that resets the label to 0. That part is complete.</p>
  
  <p>What I am having trouble with is this: I want the amounts rolled to also show up in a second UILabel that displays each roll and the sum as the buttons are tapped, until the user taps the clear button. For example, say the user tapped the d4 and got a 3, the d8 and got a 5, and the d20 and got a 12-- I would want the second UILabel to be displaying "3=3", "3+5=8", and finally "3+5+12=20". </p>
  
  <p>I know how to program the basic addition function if I was just outputting the sum itself, just not sure how to get the roll to simultaneously display in both labels along with the plus and equals signs in the second label. I don't need everything explicitly spelled out, just to be pointed in the right direction. I'm also new to stack overflow, so I apologize if I'm being too wordy or asking the wrong type of question. Thanks in advance!</p>
  
  <p><em>Edit</em> Below I have included a link to the image, as well as the text, of my code so far- very basic, as I am just learning Xcode and Swift.</p>
  
  <pre><code>import UIKit
  
  class ViewController: UIViewController {
  
      //Sum label and Roll label
      @IBOutlet weak var rollLabel: UILabel!
      @IBOutlet weak var sumLabel: UILabel!
  
      override func viewDidLoad() {
          super.viewDidLoad()
          // Do any additional setup after loading the view, typically from a nib.
      }
  
      //Dice/Clear buttons
      @IBAction func d20Tapped(_ sender: UIButton) {
          let d20Roll = arc4random_uniform(20) + 1
          rollLabel.text = "\(d20Roll)"   
      }
  
      @IBAction func d12Tapped(_ sender: UIButton) {
          let d12Roll = arc4random_uniform(12) + 1
          rollLabel.text = "\(d12Roll)"
      }
  
      @IBAction func d10Tapped(_ sender: UIButton) {
          let d10Roll = arc4random_uniform(10) + 1
          rollLabel.text = "\(d10Roll)"
      }
  
      @IBAction func d8Tapped(_ sender: UIButton) {
          let d8Roll = arc4random_uniform(8) + 1
          rollLabel.text = "\(d8Roll)"
      }
  
      @IBAction func d6Tapped(_ sender: UIButton) {
          let d6Roll = arc4random_uniform(6) + 1
          rollLabel.text = "\(d6Roll)"
      }
  
      @IBAction func d4Tapped(_ sender: UIButton) {
          let d4Roll = arc4random_uniform(4) + 1
          rollLabel.text = "\(d4Roll)"
      }
      @IBAction func clearButtonTapped(_ sender: UIButton) {
          rollLabel.text = "0"
      }
  
      override func didReceiveMemoryWarning() {
          super.didReceiveMemoryWarning()
          // Dispose of any resources that can be recreated.
      }
  }
  </code></pre>