Ray Wenderlich iOS tutorial 3; Swift has type inference

part-of-ViewController.swift

// In the View Controller the function can either declare variables upon instantiation
// or locally in the function
// But what's cooler is that you can set the function for that variable following declaration with a type specificfunction
// Like the variable difference shown here

@IBAction func showAlert() {
        // we don't have to do local instance:
        //var difference: Int
        // instead Swift just knows
        difference = currentValue - targetValue
        
        let message = "The value of the slider is: \(currentValue)" +
                        "\nThe target value is: \(targetValue)" +
                        "\n and the difference is \(difference)"
        let alert = UIAlertController(title: "hello, world", message: message, preferredStyle: .alert)
        let action = UIAlertAction(title: "Awesome", style: .default, handler: nil)
        alert.addAction(action)
        present(alert, animated: true, completion: nil)
        startNewRound()
        updateLabels()
    }