iPhone : Difference between nil vs Nil and true vs TRUE

Question

What is difference between nil and Nil in iOS development?

And similarly what is difference between true and TRUE in iOS development?

Answer 1

nil is the literal null value for Objective-C objects, corresponding to the abstract type id or any Objective-C type declared via @interface. For instance:

NSString *someString = nil;
NSURL *someURL = nil;
id someObject = nil;

if (anotherObject == nil) // do something

Nil is the literal null value for Objective-C classes, corresponding to the type Class. Since most code doesn’t need variables to reference classes, its use is not common. One example is:

 Class someClass = Nil;
 Class anotherClass = [NSString class];