What does the term "nil" mean in reference to a variable?

Whenever you customize an existing class, it is called:

A _________ file stores all information about an application's user interface objects.

Imutable objects can't be__:

True or False? Objective-C classes are objects.

The 'NS' in NSObject stands for:

In a typical Cocoa application, do you have to manage your runloop yourself?

Does Cocoa support 64bits?

What is a notification?

Is the following code valid? NSSize s = NSMakeSize(10, 10); int values[20]; values[s.height] = 5;

Can you detach threads in Cocoa?