Difference Between nil and NULL

nil is the literal null value for Objective-C objects,
NULL is the literal null value for arbitrary C pointers.

Main difference between nil & NULL is that you can send messages to nil, so you can use it in some places where NULL can't work.

The Ternary Operator (?:)

One line if statement:

int x = 23;

int y = 45;

NSLog(@"Largest number is %i", x > y ? x : y );

// logs: Largest number is 45

Getting phone UUID through iPhone SDK

//Creating UUID string with Objective C and iOS sdk

+ (NSString*) stringWithUUID {

CFUUIDRef uuidObj = CFUUIDCreate(nil);

NSString *uuidString = (NSString*)CFUUIDCreateString(nil, uuidObj);

CFRelease(uuidObj);

return [uuidString autorelease];

}

//or

[[NSProcessInfo processInfo] globallyUniqueString];