Objective-C For Dummies

When you write an Objective-C program for your iPhone or Mac OS X apps, all you are 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.

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Making an Objective-C Statement

Programming iPhone and Mac 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.

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Objective-C Built-in Data Types and New Data Types

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 iPhone 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, ... identifiern};

Identifiers are of constants of type int.

typedef

typedef  typeName  identifier;

Associates an identifier with a specific type.

Constants

const type  identifier  = value;
#define identifier value

Allows you to define names for constants.

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Objective-C Operators

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 iPhone or Mac OS X apps. Use the following tables to jog your memory as to which operator accomplishes what task.

Arithmetic Operators

Operator	What It Does
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulo

Relational and Equality Operators

Operator	What It Does
==	Equal to
!=	Not equal to
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to

Logical Operators

Operator	What It Does
!	NOT
&&	Logical AND
||	Logical OR

Compound Assignment Operators

Operator	What It Does
+=	Addition
-=	Subtraction
*=	Multiplication
\/=	Division
\%=	Modulo
&=	Bitwise AND
|=	Bitwise Inclusive OR
^=	Exclusive OR
<<=	Shift Left
>>=	Shift Right

Increment and Decrement Operators

Operator	What It Does
++	Addition
--	Subtraction
*=	Multiplication
/=	Division
%=	Modulo
&=	Bitwise AND
|=	Bitwise Inclusive OR
^=	Exclusive OR
<<=	Shift Left
>>=	Shift Right

Bitwise Operators

Operator	What It Does
&	Bitwise AND
|	Bitwise Inclusive OR
^	Exclusive OR
~	Unary complement (bit inversion)
<<	Shift Left
>>	Shift Right

Other operators

Operator	What It Does
()	Cast
,	Comma
Sizeof()	Size of
? :	Conditional
&	Address
*	Indirection

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Control Statements and Loops in Objective-C

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.

if else

if (condition) {
  statement(s) if the condition is true;
  }
else {
  statement(s) if the condition is not true;
  }

for

for (counter; condition; update counter) {
  statement(s) to execute while the condition is true;
  }

for in

for (Type newVariable in expression ) {
  statement(s); 
  }

or

Type existingVariable ;
for (existingVariable in expression) {
  statement(s);
  }

Expression is an object that conforms to the NSFastEnumeration protocol.

• An NSArray and NSSet enumeration is over content.

  
  



• An NSDictionary enumeration is over keys.

  
  



• An NSManagedObjectModel enumeration is over entities.

  
  

while

while (condition) { 
  statement(s) to execute while the condition is true 
  } 

do while

do {
  statement(s) to execute while the condition is true 
  } while (condition);

Jump statements

return ;

Stop execution and returns to the calling function.

break;

Leave a loop.

continue;

Skip the rest of the loop and start the next iteration.

goto labelName;
...
labelName: 

An absolute jump to another point in the program (don’t use it).

exit();

Terminates your program with an exit code.

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Declaring Classes and Sending Messages in Objective-C

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.

Interface

#import "Superclass.h"
@interface ClassName : Superclass {
instance variable declarations;
}
method declarations
@property(attributes) instance variable declaration;
–d

Implementation

#import "ClassName.h"
@implementation ClassName
@synthesize instance variable ;
method definitions
–d

Message Syntax

[receiver message]

#import

#import “filename.h”

Guarantees that a header file will be included only once.

@class

@class ClassName;

Clues the compiler into user defined types.

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