Cheat Sheet

Objective-C Programming For Dummies

When you write an Objective-C program for your iOS or Mac OS X apps in Objective-C, 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.

Making an Objective-C Statement

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 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 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, ... 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.

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 iOS 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
++ Increment
-- Decrement
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

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 return 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.

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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