Programming iOS 4

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; 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. The usual convention is thus to declare a variable and assign it a value as it makes its first appearance on the scene:

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. iOS makes use of some further numeric types derived from the C numeric types (by way of the typedef statement, K&R 6.7); the most important of these are NSInteger (along with NSUInteger) and CGFloat. You don’t need to use these 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 be fine.

To cast (or typecast) a variable’s value explicitly to another type, precede the variable’s name with the other type’s name in parentheses:

int height = 2; float ...