Swift - How to generate random numbers between two numbers?

I'm trying to learn swift by myself so sorry if this turns out to be very simple.

I want to make a function that, given two numbers (example: 5, 60) gives back random numbers between those two numbers (example: 33,56,12, but not 2 or 90).

I tried using this line of code on the Playground and it worked

var a : UInt32
var b : UInt32
a = 5
b = 60
let randomNumber = arc4random_uniform(b-a) + a
//gives back a random number between 5 and 60

However, when I create - using the same method - the function randomNumberInBetween in my viewController.swift, it gives me an error.

var a = UInt32()
var b = UInt32()
var randomNumberInBetween = Int()

func randomInBetween() {
    randomNumberInBetween = Int(arc4random_uniform(b - a) + a)
    // here I get this error:   Thread 1 : EXC_BAD_INSTRUCTION (code=EXC_l386_INVOP,subcode=0x0)
}



@IBAction func TextAAction(sender: AnyObject) {
    a = UInt32(TextA.text!)!
}


@IBAction func TextBAction(sender: AnyObject) {
    b = UInt32(TextB.text!)!
}


@IBAction func randomInBetweenAction(sender: AnyObject) {
    randomInBetween()
    unHide()
    Label.text = "\(randomInBetween)"
    NSLog("\(randomInBetween)")
}

(PS: TextA is a Text field in which the user inserts the value a (ex: 5) TextB is a Text field in which the user inserts the value b (ex: 60) )

I've been trying to work it out by myself but I just lost hope, anyone knows what the problem is? Thank you:)