Objective-C Basic Syntax

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You have seen a basic structure of Objective-C program, so it will be easy to understand other basic building blocks of the Objective-C programming language.

Tokens in Objective-C

A 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 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, 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 with in 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:

mohd       zara    abc   move_name  a_123
myname50   _temp   j     a23b9      retVal

Keywords

The following list shows few of the reserved words in Objective-C. These reserved words may not be used as constant or variable or any other identifier names.

auto else long switch
break enum register typedef
case extern return union
char float short unsigned
const for signed void
continue goto sizeof volatile
default if static while
do int struct _Packed
double protocol interface implementation
NSObject NSInteger NSNumber CGFloat
property nonatomic; retain strong
weak unsafe_unretained; readwrite readonly

Whitespace in Objective-C

A line containing only whitespace, possibly with a comment, is known as a blank line, and an Objective-C compiler totally ignores it.

Whitespace is the term used in Objective-C to describe blanks, tabs, newline characters and comments. Whitespace separates one part of a statement from another and enables the compiler to identify where one element in a statement, such as int, ends and the next element begins. Therefore, in the following statement:

int age;

There must be at least one whitespace character (usually a space) between int and age for the compiler to be able to distinguish them. On the other hand, in the following statement,

fruit = apples + oranges;   // get the total fruit

no whitespace characters are necessary between fruit and =, or between = and apples, although you are free to include some if you wish for readability purpose.



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