Programming iOS 6, 3rd Edition

Operators

Arithmetic operators are straightforward (K&R 2.5), but watch out for the rule that “integer division truncates any fractional part.” This rule is the cause of much novice error in C. If you have two integers and you want to divide them in such a way as to get a fractional result, you must represent at least one of them as a float:

int i = 3;
float f = i/2; // beware! not 1.5

To get 1.5, you should have written i/2.0 or (float)i/2.

The integer increment and decrement operators (K&R 2.8), ++ and --, work differently depending on whether they precede or follow their variable. The expression ++i replaces the value of i by 1 more than its current value and then uses the resulting value; the expression i++ uses the current value of i and then replaces it with 1 more than its current value. This is one of C’s coolest features.

C also provides bitwise operators (K&R 2.9), such as bitwise-and (&) and bitwise-or (|); they operate on the individual binary bits that constitute integers. Of these, the one you are most likely to need is bitwise-or, because the Cocoa API often uses bits as switches when multiple options are to be specified simultaneously. For example, there are various ways in which a UIView can be resized automatically as its superview is resized, and you’re supposed to provide one or more of these when setting a UIView’s autoresizingMask property. The autoresizing options are listed in the documentation as follows:

typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) { UIViewAutoresizingNone ...