Programming iOS 6, 3rd Edition

Variable Declaration, Initialization, and Data Types

C is a strongly typed language. Every variable must be declared, indicating its data type, before it can be used. Declaration can also involve explicit initialization, giving the variable a value; a variable that is declared but not explicitly initialized is of uncertain value (and should be regarded as dangerous until it is initialized). In K&R C, declarations must precede all other statements, but in modern versions of C, this rule is relaxed so that you don’t have to declare a variable until just before you start using it:

int height = 2;
int width = height * 2;
height = height + 1;
int area = height * width;

The basic built-in C data types are all numeric: char (one byte), int (four bytes), float and double (floating-point numbers), and varieties such as short (short integer), long (long integer), unsigned short, and so on. A numeric literal may optionally express its type through a suffixed letter or letters: for example, 4 is an int, but 4UL is an unsigned long; 4.0 is a double, but 4.0f is a float. Objective-C makes use of some further numeric types derived from the C numeric types (by way of the typedef statement, K&R 6.7) designed to respond to the question of whether the processor is 64-bit; the most important of these are NSInteger (along with NSUInteger) and CGFloat. You don’t need to use them explicitly unless an API tells you to, and even when you do, just think of NSInteger as int and CGFloat as float, and you’ll ...