What's the difference between nil and NULL?

How is a selector typically represented in memory?

Which of these methods is NOT invoked by the runtime itself?

A UIView is a superclass of:

What happens at runtime with the following: NSMutableString *tempString = [NSMutableString stringWithString:@"1"]; dispatch_sync(dispatch_get_main_queue(), ^{ [tempString appendString:@"2"]; NSLog(@"%@", tempString); }); [tempString appendString:@"3"];

What happens if two categories define methods with the same names for the same class?

Which one is the base class of all objects in Objective-c ?

Which method creates and returns an NSNumber object containing a given value, treating it as an NSInteger.

While calling a function by reference, it will copy the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. Is the statement above True ?

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the (...) programming language

What happens when the following code executes?