T-rain

class ViewController: UIViewController {

    @IBOutlet weak var numPad: UILabel!
    //下面這行會報錯：Instance member 'numPad' cannot be used on type 'ViewController'
    var num_pad_text_error = numPad.text
    
    @IBAction func clickOperator(sender: UIButton) {
        
        let operator_text :String = sender.titleLabel!.text!