I'm getting the error "unrecognized selector sent to instance" - swift

Question

When I try to press on any button on my calculator it gives me the error unrecognized selector sent to instance 0x7f7f85e04e40 I updated this code from Swift 2 to Swift 4 but back then it used to work. What's wrong with the code?
import UIKit
class Valuta: UIViewController {
#IBOutlet weak var euro: UILabel!
#IBOutlet weak var zloty: UILabel!
#IBOutlet weak var topButton: UIButton!
#IBOutlet weak var bottomButton: UIButton!
var valutas : [ValutaWaarde] = []
var number = 0;
var isTypingNumber = false
var currentNumber = 0;
var currency = "PLN";
#IBAction func numberTapped(sender: AnyObject) {
let number = sender.currentTitle!
var disable = false
if number == "."{
if euro.text!.range(of: ".") != nil{
disable = true
}
}
if(disable == false){
if isTypingNumber {
euro.text = euro.text!+number!
} else {
euro.text = number
isTypingNumber = true
}
var output : Float;
if(currency == "EUR"){
output = (euro.text! as NSString).floatValue*Float((valutas[0].rates?.pLN!)!)
}
else{
output = (euro.text! as NSString).floatValue/Float((valutas[0].rates?.pLN!)!)
}
zloty.text = String(format: "%.2f", output)
}
}
#IBAction func resetCalculator(sender: AnyObject) {
isTypingNumber = false;
zloty.text = "0";
euro.text = "0";
}
override func viewDidLoad() {
super.viewDidLoad()
UINavigationBar.appearance().isTranslucent = false;
UINavigationBar.appearance().barTintColor = UIColor(red: CGFloat(51/255.0), green: 51/255, blue: 51/255, alpha: 1)
UINavigationBar.appearance().titleTextAttributes = [NSAttributedStringKey.foregroundColor:UIColor.white]
//Get list
let url = URL(string: "https://api.fixer.io/latest?symbols=PLN&base=EUR")
var request = NSMutableURLRequest(url: url! as URL, cachePolicy: NSURLRequest.CachePolicy.returnCacheDataElseLoad, timeoutInterval: Double.infinity)
if Reachability.isConnectedToNetwork(){
request = NSMutableURLRequest(url: url! as URL, cachePolicy: NSURLRequest.CachePolicy.useProtocolCachePolicy, timeoutInterval: Double.infinity);
}
let session = URLSession.shared
let task = session.dataTask(with: request as URLRequest,
completionHandler: { data, response, error -> Void in
do {
if let json = try JSONSerialization.jsonObject(with: data!) as? [[String: String]] {
for valutaData in json {
let valuta = ValutaWaarde(dictionary: valutaData as NSDictionary)
self.valutas.append(valuta!)
}
}
} catch { print(error) }
})
task.resume()
}
...
}

Answer 1

Try to re-connect #IBOutlets and #IBActions in storyboard.