why when you initialize array using initWithObjects the last item is "nil"?

Question

Possible Duplicate:
NSArray creation with variable argument lists in Objective-C

that's it actually the question is very simple. Xcode suggests that the last item is "nil" and I was wondering why.

array1 = [[NSArray alloc] initWithObjects: @"one", @"two", @"three", @"four", nil];

Answer 1

A null-termination (nil) character is used to determine the length of an array. Failure to properly terminate an array can result in buffer overflows and other undefined behavior.

Answer 2

Aside from redirecting to the docs about NSArray initWithObjects, it is worth noting that in general, with variadic functions (i.e. functions that take a variable number of arguments), either you specify the number of arguments upfront, or you terminate the argument list in some way. Nil is a good way of terminating the argument list and is the approach taken with initWithObjects.