Difference between objectAtIndex and [0]

Question

What is the difference between using the following:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *dir = [paths objectAtIndex:0]; 

    NSString *dir2 = paths[0]; // this throws incompatible type exception

Answer 1

1. paths is a pointer to instance of NSArray that you are sending the objectAtIndex: message. The receiver returns an id.
2. paths[0] is the memory address of the beginning of an array in pure C. [] and NSArray are not the same thing.