import UIKit

class ThirdViewController: UIViewController {

var order1Text = String()
var myOrder = OrderModel()

override func viewDidLoad() {
    super.viewDidLoad()

    let barViewControllers = self.tabBarController?.viewControllers
    let svc = barViewControllers![1] as SecondViewController //error here
    svc.myOrder = self.myOrder

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()

}

override func viewWillAppear(animated: Bool) {
    order1Label.text = myOrder.currentOrder()

}

@IBOutlet var order1Label: UILabel!

}