Unexpectedly found nil when using variable outside of declared function - swift

Question

I am trying to make a kind of maths games where when an enemy is shot the user is prompted with a maths question, I made it so when an enemy is shot a keypad with numbers pops up where the user enters the answer. But whenever the keypad pops up I get the error:
Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
At the top of the code I have declared the the variables I am using:
var button1:SKLabelNode?
var answerDisplay:SKLabelNode!
This is the function that runs when the enemy is shot:
func runMathsProblem(){
//This is the label that is meant to display what the user enters
let answerDisplay = SKLabelNode(fontNamed: "Bulky Pixels")
answerDisplay.name = "AnswerDisplay"
answerDisplay.text = "= "
answerDisplay.fontSize = 110
answerDisplay.fontColor = SKColor.white
answerDisplay.horizontalAlignmentMode = SKLabelHorizontalAlignmentMode.left
answerDisplay.zPosition = 110
answerDisplay.position = CGPoint(x: self.size.width * 0.38, y: self.size.height * 0.63)
self.addChild(answerDisplay)
//This is the button the user presses to type "1" on screen
let button1 = SKLabelNode(fontNamed: "Bulky Pixels")
button1.name = "Button1"
button1.text = "1"
button1.fontSize = 110
button1.fontColor = SKColor.white
button1.zPosition = 120
button1.position = CGPoint(x: self.size.width * 0.3, y: self.size.height * 0.32)
self.addChild(button1)
}
This is where it detects if the user has pressed a button and is meant to to add the number pressed to the variable answerDisplay to display on screen(this is also where I get the error):
override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
for touch: AnyObject in touches{
let pointOfTouch = touch.location(in: self)
if button1!.contains(pointOfTouch){ **//This is where I get the error**
answerDisplay!.text = answerDisplay.text! + "1"
}
}
}
I think it is something to do with the way I have declared the variable

Answer 1

At the top of the code I have declared the the variables I am using
But you never end up using them, because...
let answerDisplay = SKLabelNode(fontNamed: "Bulky Pixels")
.
.
.
let button1 = SKLabelNode(fontNamed: "Bulky Pixels")
.
.
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This creates new instances of SKLabelNode instead of using the ones you already created. So, what you need to do is remove the keyword let so that the compiler understands that you are referring to the variables that you already declared.