func makePopup(popupTitle:String, popupMessage:String) {
        
        let controller = UIAlertController(
            title: popupTitle,
            message: popupMessage,
            preferredStyle: .alert)
        
        controller.addAction(UIAlertAction(title: "OK", style: .default))
        
        present(controller,animated:true)
    }

// Call it this way:

    makePopup(popupTitle: "Error:", popupMessage: "You didn't enter a value")