What is a Variable? How to Declare and Assign values to Variables?

Variable: Variable is a named memory location that can store some value unlike constants a Variable may take different values at different times during execution. A Variable name can be chosen by the programmer in a meaningful way.            Variable names may consist of letters, digits & the underscore character.

Rules for declaring Variable:

They must begin with a letter.

ANSI standard recognizes a length of 31 characters. However, length should not be normally more than eight characters, since only the 1st eight characters are treated as significant by may compilers.

Upper case & lower case letters are different i.e. ‘A’ is not the same as ‘a’ .

It should not be a keyword.

White space is not allowed

Declaration of a Variable: After designing suitable Variable names, we must declare then to the compiler. Declaration does (or tells) 3 things.

1. It tells the compiler what the Variable name is. 2. It specifies what type of data the Variable will hold. 3. The place of declaration decides the scope of Variable In the program. The declaration of Variables must be done before they are used in the program. A Variable can be used to store a value of any data type. Syntax: datatype V1, V2,………Vn; V1, V2,………Vn are the names of Variable. Variables are separated by commas. A declration statement must end with a semicolon. Ex:  int number, total;        Float ratio;

Assigning values to Variables:

Variables must be given a value after it has been declared & before it is used in any expression.It can be done in 2 ways: 1. By using an assignment statement. 2. Reading data from keyboard (using scanf( ) statement.) Assignment statement: Values can be assigned to Variables using the assignment operator = as follows. Syntax:Variable_name = constant; Ex : initial_balance = 0;         Balance = 75.84;         yes = ‘x’; C permits multiple assignments in one line Ex: initial_value = 0; final_value = 100; It is also possible to assign a value to a Variable at the time the Variable is declared. Syntax: datatype Variable_name = constant; Ex :  int final_value = 100;         double balance = 72.82; The process of giving initial values to Variables is called initialization. C permits the initialization of more than one Variables in one statement using multiple assignment operators. Ex :  p = q = r = 0;           The first statement initializes the Variables p, q & r to 0. Reading data from keyboard: Another way of giving values to Variable is to input data through keyboard using the scanf function. Syntax: scanf (“ control string”, &Variable1, &Variable2, …..);  The ampersand symbol & before each Variable name is an operator that specifies the Variable name’s address. Ex: scanf  (“ % d”, & no); When this statement is encountered by the computer, the execution stops & waits for the value of the Variable no. to be typed in. since the control string %d specifies that an integer value is to be read from the terminal.