App not working when I try to load it

Question

When I try to load the random number changes my app won't load and I am prompted with an error to change var to let.  Does any one know why?  This is what I have in factbook.swift: 
import Foundation
struct FactBook {
    let factsArray = [ "Ants stretch when they wake up in the morning.",
        "Ostriches can run faster than horses.",
        "Olympic gold medals are actually made mostly of silver.",
        "You are born with 300 bones; by the time you are an adult you will have 206.",
        "It takes about 8 minutes for light from the Sun to reach Earth.",
        "Some bamboo plants can grow almost a meter in just one day.",
        "The state of Florida is bigger than England.",
        "Some penguins can leap 2-3 meters out of the water.",
        "On average, it takes 66 days to form a new habit.",
        "Mammoths still walked the earth when the Great Pyramid was being built." ]
func randomFact() -> String {
    var unsignedArrayCount = UInt32(factsArray.count)
    var unsignedRandomNumber = arc4random_uniform(unsignedArrayCount)
    var randomNumber = Int(unsignedRandomNumber)

return factsArray[randomNumber]
}
}
This is what I have in my view controller: 
import UIKit
class ViewController: UIViewController {
    @IBOutlet weak var funFactLabel: UILabel!
let factBook = FactBook()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    funFactLabel.text = factBook.randomFact()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func showFunFact() {
    funFactLabel.text = factBook.randomFact()
}
}

Richard Lu · Answer

So from what I understand, your question is why XCode is prompting you to change your var to a let. The reason comes directly from Apples documentation 
"If a stored value in your code is not going to change, always declare it as a constant with the let keyword. Use variables only for storing values that need to be able to change."
Source: http://tinyurl.com/mlw75pm
In your case factBook never changes.
```swift
import UIKit
class ViewController: UIViewController { 
   @IBOutlet weak var funFactLabel: UILabel!
   let factBook = FactBook()   // THIS NEVER CHANGES 
   override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
      funFactLabel.text = factBook.randomFact()   // IT IS ONLY UTILIZED
   }
   override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
   }
   @IBAction func showFunFact() {
      funFactLabel.text = factBook.randomFact()
   }
}
```
I hope I've helped :)

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Victoria M

Victoria M

App not working when I try to load it

1 Answer

Richard Lu

Richard Lu