Identifiers & variables

Identifier:-

The C identifier is a name used to identify a variable, function, class, module, 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).

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

Here are some examples of acceptable identifiers −

mohd	Piyush	abc	move_name	a_123
myname50	_temp	j	a23b9	retVal

Types:

            There are two types of identifiers:

·         Standard identifiers.

·         User-defined identifiers.

Standard identifiers:

            Like reserved words, standard identifiers have special meaning in C, but these can be redefined to use in the program for other purpose, however this practice is not recommended.

User-defined identifiers:

            User need to access memory locations for storing data and program results. For this purpose memory cells named that are called user-defined identifiers.

*C is a case sensitive language. So, SQUARE_AREA and square_area are two different identifiers.

Keyword:

            Keyword or reserved words are the words, which have pre-defined meaning in any high level programming language.

Variable

            Variables are named memory location (memory cells), which are used to store program’s input and its computational results during program execution.

The variables are created in memory (RAM) therefore the data is stored in them temporarily.

Declaration:

            In C all variables are must declare before being used. The compiler report an error if any undeclared variable is used.

A variable is declared by specified its type (data type) and name.

·         A variable declaration does not set aside memory location for the data to be stored.

·         It just informs the compiler the name of variable and its data type.

Syntax:

            Data type        variable name;

Example:

            Int number;

Definition:

            “In definition of variable that set aside the location of variable in memory.“

Initializing the variable:

                        “Assigning a value to a variable at the time of its declaration is called initializing a variable.”  

Garbage Value:

            When a variable is declared, the compiler set aside some memory space for it. This allocation memory space may contain data meaningless to the program called garbage value.

Rules of naming Variable

·         A variable name consists of letters, numbers and underscore.

·         The first character is must be letter.

Example: home#2, winner_2 are valid.

             #home, 2winner are invalid.

·         C is a case sensitive language. So, SQUARE_AREA and square_area are two different variables.

·         Keywords are not used as variables.

·         First 31 characters are significant. If two variables has first 31 characters are same so the compiler cannot be recognized difference between them.

·         Blank spaces are not allowed between the names of variable.

·         A variable can only declared for one data type.