Question

I recently started following the online course on iPhone development from Stanford University on iTunes U.

I’m trying to do the homework assignments now for the first couple of lectures. I followed through the walkthrough where I built a basic calculator, but now I’m trying the first assignment and I can’t seem to work it out. It’s a follows:

Add a “C” button that clears everything (for example, the display in your View, the operand stack in your Model, any state you maintain in your Controller, etc.). Make sure 3 7 C 5 results in 5 showing in the display. You will have to add API to your Model to support this feature.

What API do i need to add?

I tried something like this:

- (IBAction)CancelPressed {
    self.Display.text = 0;
}

I know this is wrong. I need some guidance. Thanks in advance..Sorry if the question is stupid..

Answer 1

I am also going through the fall 2011 version on iTunesU. Here is the way I accomplished this.

- (IBAction)clearPressed {
    self.display.text = @"0";
    self.userIsInTheMiddleOfEnteringANumber = NO;
    self.brain = nil;
}

The only thing is I actually did not have to add API to my model. Because the controller has a CalculatorBrain instance variable I just toss that out, and since we lazily instantiated our brain getter, I’ll get a brand new one (already cleared) next time I call the getter.