Beginner friendly Objective-c tutorial

About Objective-C

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. This is the main programming language used by Apple for the OS X and iOS operating systems and their respective APIs, Cocoa and Cocoa Touch. This reference will take you through a simple and practical approach while learning Objective-C Programming language.

Prerequisites

Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware of what is a computer program and what is a computer programming language?

Objective-C is a general-purpose language that is developed on top of C Programming language by adding features of Small Talk programming language making it an object-oriented language. It is primarily used in developing iOS and Mac OS X operating systems as well as its applications.

Initially, Objective-C was developed by NeXT for its NeXTSTEP OS from whom it was taken over by Apple for its iOS and Mac OS.

What is Object-Oriented Programming and Types?

Objective-C fully supports object-oriented programming, including the four pillars of object-oriented development −

1. Encapsulation

2. Data hiding

3. Inheritance

4. Polymorphism

For Example:

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {

   NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

   NSLog (@"hello world");

   [pool drain];

   return 0;

}

Foundation Framework

Foundation Framework provides a large set of features and they are listed below:

1. It includes a list of extended datatypes like NSArray, NSDictionary, NSSet, and so on.

2. It consists of a rich set of functions manipulating files, strings, etc.

3. It provides features for URL handling, utilities like date formatting, data handling, error handling, etc.

Learning Objective-C

The most important thing to do when learning Objective-C is to focus on concepts and not get lost in language technical details.

The purpose of learning a programming language is to become a better programmer; that is, to become more effective at designing and implementing new systems and at maintaining old ones.

Use of Objective-C

Objective-C, as mentioned earlier, is used in iOS and Mac OS X. It has a large base of iOS users and largely increasing Mac OS X users. And since Apple focuses on quality first and it is wonderful for those who started learning Objective-C.

Local Environment Setup

If you are still willing to set up your own environment for Objective-C programming language, then you need to install Text Editor and The GCC Compiler on your computer.

Text Editor

This will be used to type your program. Examples of few editors include Windows Notepad, OS Edit command, Brief, Epsilon, EMACS, and vim or vi.

The name and version of the text editor can vary on different operating systems. For example, Notepad will be used on Windows, and vim or vi can be used on windows as well as Linux or UNIX.

The files you create with your editor are called source files and contain program source code. The source files for Objective-C programs are typically named with the extension ".m".

Before starting your programming, make sure you have one text editor in place and you have enough experience to write a computer program, save it in a file, compile it and finally execute it.

The GCC Compiler

The source code written in a source file is the human-readable source for your program. It needs to be "compiled" to turn into machine language so that your CPU can actually execute the program as per the instructions given.

This GCC compiler will be used to compile your source code into the final executable program. I assume you have basic knowledge about a programming language compiler.

GCC compiler is available for free on various platforms and the procedure to set up on various platforms is explained below.

Installation Process for Windows:

2021-07-28 10:48:39.772 codeschoolspy[200] hello world

Objective-C Hello World Example

An Objective-C program basically consists of the following parts −

1. Preprocessor Commands

2. Interface

3. Implementation

4. Method

5. Variables

6. Statements & Expressions

7. Comments

Let us look at a simple code that would print the words "Hello World" −

#import <Foundation/Foundation.h>

@interface SampleClass:NSObject

- (void)sampleMethod;

@end

@implementation SampleClass

- (void)sampleMethod {

   NSLog(@"Hello, World! \n");

}

@end

int main() {

   /* my first program in Objective-C */

   SampleClass *sampleClass = [[SampleClass alloc]init];

   [sampleClass sampleMethod];

   return 0;

}

Let us look at various parts of the above program −

The first line of the program #import <Foundation/Foundation.h> is a preprocessor command, which tells an Objective-C compiler to include Foundation.h file before going to actual compilation.

The next line @interface SampleClass: NSObject shows how to create an interface. It inherits NSObject, which is the base class of all objects.

1. The next line - (void)sampleMethod; shows how to declare a method.

2. The next line @end marks the end of an interface.

3. The next line @implementation SampleClass shows how to implement the interface SampleClass.

4. The next line - (void)sampleMethod{} shows the implementation of the sampleMethod.

5. The next line @end marks the end of an implementation.

6. The next line int main() is the main function where program execution begins.

7. The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program. So such lines are called comments in the program.

8. The next line NSLog(...) is another function available in Objective-C which causes the message "Hello, World!" to be displayed on the screen.

9. The next line return 0; terminates main()function and returns the value 0.

Compile & Execute Objective-C Program

Now when we compile and run the program, we will get the following result.

2021-07-28 07:48:32.020 trial[249634] Hello, World!

Tokens in Objective-C

An Objective-C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. For example, the following Objective-C statement consists of six tokens −

NSLog(@"Hello, World! \n");

The individual tokens are −

NSLog

@

(

   "Hello, World! \n"

)

;

Semicolons ;

In the Objective-C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

For example, the following are two different statements −

NSLog(@"Hello, World! \n");

return 0;

Comments

Comments are like helping text in your Objective-C program and they are ignored by the compiler. They start with /* and terminate with the characters */ as shown below −

/* my first program in Objective-C */

You can not have comments within comments and they do not occur within a string or character literals.

Identifiers

An Objective-C identifier is a name used to identify a variable, function, or any other user-defined item. An identifier starts with a letter A to Z or a to z or an underscore _ followed by zero or more letters, underscores, and digits (0 to 9).

Objective-C does not allow punctuation characters such as @, $, and % within identifiers. Objective-C is a case-sensitive programming language. Thus, Manpower and manpower are two different identifiers in Objective-C. Here are some examples of acceptable identifiers −

Mohammad      Zara    ABC   move_name  a_123

myname50   _temp   j     a23b9      retVal

The types in Objective-C can be classified as follows −

Basic Types −

They are arithmetic types and consist of two types: (a) integer types and (b) floating-point types.

Enumerated types −

They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program.

The type void −

The type specifier void indicates that no value is available.

Derived types −

They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types.

Integer Types

The following table gives you details about standard integer types with their storage sizes and value ranges −

Type                                                     Storage Size                                              Value Range

char                                                        1 byte                                             -128 to 127 or 0 to 255

unsigned char                                         1 byte                                             0 to 255

signed char                                             1 byte                                             -128 to 127

int                                                           2 or 4 bytes                                    -32,768 to 32,767 or -2,147,483,648 

unsigned int                                            2 or 4 bytes                                    0 to 65,535 or 0 to 4,294,967,295

short                                                        2 bytes                                           -32,768 to 32,767

unsigned sort                                           2 bytes                                            0 to 65,535

long                                                          4 bytes                                           -2,147,483,648 to 2,147,483,647

unsigned long                                           4 bytes                                            0 to 4,294,967,295

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in Objective-C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because Objective-C is case-sensitive. Based on the basic types explained in the previous chapter, there will be the following basic variable types −

char

Typically a single octet (one byte). This is an integer type.

int

The most natural size of integer for the machine.

float

A single-precision floating-point value.

double

A double-precision floating-point value.

void

Represents the absence of type.

The Objective-C programming language also allows defining various other types of variables, which we will cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union, etc. For this chapter, let us study only basic variable types.

Variable Definition in Objective-C

A variable definition means to tell the compiler where and how much to create the storage for the variable. A variable definition specifies a data type and contains a list of one or more variables of that type as follows −

type variable_list;

Here, the type must be a valid Objective-C data type including char, w_char, int, float, double, bool or any user-defined object, etc., and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here −

int    i, j, k;

char   c, ch;

float  f, salary;

double d;

The line int i, j, k; both declares and defines the variables i, j, and k; which instructs the compiler to create variables named i, j, and k of type int.

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows −

type variable_name = value;

Some examples are −

extern int d = 3, f = 5;    // declaration of d and f. 

int d = 3, f = 5;           // definition and initializing d and f. 

byte z = 22;                // definition and initializes z. 

char x = 'x';               // the variable x has the value 'x'.

For definition without an initializer: variables with static storage duration are implicitly initialized with NULL (all bytes have the value 0); the initial value of all other variables is undefined.

Variable Declaration in Objective-C

A variable declaration provides assurance to the compiler that there is one variable existing with the given type and name so that compiler proceeds with further compilation without needing complete detail about the variable. A variable declaration has its meaning at the time of compilation only, the compiler needs actual variable declaration at the time of linking of the program.

A variable declaration is useful when you are using multiple files and you define your variable in one of the files, which will be available at the time of linking the program. You will use the extern keyword to declare a variable at any place. Though you can declare a variable multiple times in your Objective-C program it can be defined only once in a file, a function, or a block of code.

Example

Try the following example, where variables have been declared at the top, but they have been defined and initialized inside the main function −

#import <Foundation/Foundation.h>

// Variable declaration:

extern int a, b;

extern int c;

extern float f;

int main () {

  /* variable definition: */

  int a, b;

  int c;

  float f;

   /* actual initialization */

  a = 10;

  b = 20;

    c = a + b;

  NSLog(@"value of c : %d \n", c);

  f = 70.0/3.0;

  NSLog(@"value of f : %f \n", f);

   return 0;

}

When the above code is compiled and executed, it produces the following result −

2021-07-28 22:43:31.695 demo[14019] value of c : 30 

2021-07-28 22:43:31.695 demo[14019] value of f : 23.333334 

The same concept applies to function declaration where you provide a function name at the time of its declaration and its actual definition can be given anywhere else. In the following example, it's explained using the C function and as you know Objective-C supports C style functions also −

// function declaration

int func();

int main() {

   // function call

   int i = func();

}

// function definition

int func() {

   return 0;

}

L values and R values in Objective-C

There are two kinds of expressions in Objective-C −

L value − Expressions that refer to a memory location are called "L Value" expressions. An lvalue may appear as either the left-hand or right-hand side of an assignment.

R value − The term R value refers to a data value that is stored at some address in memory. An rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right- but not the left-hand side of an assignment.

Variables are L values and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement −

int g = 20;

But following is not a valid statement and would generate a compile-time error −

10 = 20;

Objective-C Constants

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals.

Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer Literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals −

212         /* Legal */

215u        /* Legal */

0xFeeL      /* Legal */

078         /* Illegal: 8 is not an octal digit */

032UU       /* Illegal: cannot repeat a suffix */

Following are other examples of various types of Integer literals −

85         /* decimal */

0213       /* octal */

0x4b       /* hexadecimal */

30         /* int */

30u        /* unsigned int */

30l        /* long */

30ul       /* unsigned long */

Floating-point Literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

While representing using the decimal form, you must include the decimal point, the exponent, or both and while representing using the exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Here are some examples of floating-point literals −

3.14159       /* Legal */

314159E-5L    /* Legal */

510E          /* Illegal: incomplete exponent */

210f          /* Illegal: no decimal or exponent */

.e55          /* Illegal: missing integer or fraction */

Character Constants

Character literals are enclosed in single quotes e.g., X, and can be stored in a simple variable of char type.

A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').

There are certain characters in C when they are proceeded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes −

Escape sequence     Meaning

\\                            \ character

\'                            ' character

\"                            " character

\?                            ? character

\a                            Alert or bell

\b                            Backspace

\f                            Form feed

\n                            Newline

\r                            Carriage return

\t                            Horizontal tab

\v                            Vertical tab

\ooo                            Octal number of one to three digits

\xhh . . .                    Hexadecimal number of one or more digits

Following is the example to show few escape sequence characters −

#import <Foundation/Foundation.h>

int main() {

   NSLog(@"Hello\tWorld\n\n");

   return 0;

}

When the above code is compiled and executed, it produces the following result −

2021-07-28 22:17:17.923 demo[17871] Hello World

String Literals

String literals or constants are enclosed in double-quotes "". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters. You can break a long line into multiple lines using string literals and separating them using whitespaces.

Here are some examples of string literals. All three forms are identical strings:

"Hello, dear"

"Hello, \dear"

"Hello, " "d" "ear"

Defining Constants

There are two simple ways in C to define constants −

1. Using #define preprocessor.

2. Using const keyword.

The #define Preprocessor

Following is the form to use #define preprocessor to define a constant −

#define identifier value

The following example explains it in detail −

#import <Foundation/Foundation.h>

#define LENGTH 10   

#define WIDTH  5

#define NEWLINE '\n'

int main() {

   int area;

   area = LENGTH * WIDTH;

   NSLog(@"value of area : %d", area);

   NSLog(@"%c", NEWLINE);

   return 0;

}

When the above code is compiled and executed, it produces the following result −

2013-09-07 22:18:16.637 demo[21460] value of area : 50

2013-09-07 22:18:16.638 demo[21460] 

The const Keyword

You can use the const prefix to declare constants with a specific type as follows −

const type variable = value;

The following example explains it in detail −

#import <Foundation/Foundation.h>

int main() {

   const int  LENGTH = 10;

   const int  WIDTH  = 5;

   const char NEWLINE = '\n';

   int area;  

   area = LENGTH * WIDTH;

   NSLog(@"value of area : %d", area);

   NSLog(@"%c", NEWLINE);

   return 0;

}

When the above code is compiled and executed, it produces the following result −

2021-07-28 22:19:24.780 demo[25621] value of area : 50

2021-07-28 22:19:24.781 demo[25621]