Neal Goldstein

When you write an Objective-C program for your iOS or Mac OS X apps, all you're doing is providing a set of instructions for the computer to follow. Fundamentally, programs manipulate numbers and text, and all things considered, a computer program has only two parts: variables (and other structures), which "hold" the data, and instructions, which perform operations on that data.

In programming, as in life, you have to make decisions and act on them. Objective-C provides control statements and loops to help your program take action. You may want to repeat a set of instructions based on some condition or state, for example, or even change the program execution sequence. Here is the basic syntax for Objective-C control statements and loops.

Programming iOS and Mac OS X apps in Objective-C is about making a statement. You can recognize a statement in Objective-C immediately by noting the semicolon at the end: statement; You will see other lines of code, but unless the line ends with a semicolon, it is not an Objective-C statement.

Objective-C operators, like those in other programming languages, let you perform operations on variables (hence the name). Objective-C provides many operators, and keeping track of all of them can be difficult as you program your iOS or Mac OS X apps. Use the following tables to jog your memory as to which operator accomplishes what task.

Object-oriented programming languages enable you to declare classes, create derived classes (subclass), and send messages to the objects instantiated from a class. This is the essence of object-oriented programming and part of the object-oriented extensions that Objective-C adds to C. To ensure that everything operates smoothly, compiler directives are available that enable you to inform the compiler of your classes by using @class and #import.

The variables you declare in Objective-C — Objective-C data types — must be a type that the compiler can recognize. Objective-C comes with a number of built-in data types, as well as mechanisms to create new ones, for programming your iOS or Mac OS X applications. Built-In Types Type Description Size char A character 1 byte int An integer — a whole number 4 bytes float Single precision floating point number 4 bytes double Double precision floating point number 8 bytes short A short integer 2 bytes long A double short 4 bytes long long A double long 8 bytes BOOL Boolean (signed char) 1 byte Enumeration types enum typeName { identifier1, .