Making Decisions(Chapter 6 of Programming in Objective-C 2.0)

　　This is because the conditional operator associates from right to left, meaning that multiple uses of this operator in a single expression, such as in

　　e1 ? e2 : e3 ? e4 : e5

　　group from right to left and therefore are evaluated as follows:

　　e1 ? e2 : ( e3 ? e4 : e5 )