Code is right (according to tutorial) but I still get a CS0428 error?

So I was following a GUI Button related tutorial for Unity 5+ and I copy the code on it exactly like it displayed, like this:

void Start ()
	{
		mainMenu = mainMenu.GetComponent <Canvas>;
		startButton = startButton.GetComponent <Button>;
		quitButton = quitButton.GetComponent <Button>;

	}

but, unlike the tutorial, I get this error:

WHY?

I dont see anything actually wrong with the tutorial nor the code I wrote myself. Why is this happening? Am I missing something?

(They are all stated as public right before void Start, btw. )

Thanks in advance!

The parenthesis are missing. Check this:

void Start ()
{
    mainMenu = mainMenu.GetComponent<Canvas>();
    startButton = startButton.GetComponent<Button>();
    quitButton = quitButton.GetComponent<Button>();
}