A variable is a name assigned to some storage area in a memory allocated to it. In other words a variable is a value which can be altered during the program execution.

Syntax:
type variable_name;
Example:
int length, width = 10;
float value;

Rules for naming a variable

  1. The first character of an variable should be a alphabet(a-z , A-Z) or underscore (_).
  2. Keywords are not allowed to be used as variable.
  3. Variable should not be of length more than 31 characters.
  4. Commas or spaces are not allowed within an identifier.
  5. Variable are case-sensitive so UPPERCASE and lowercase are treated as different name. For example: APPLE, Apple and apple are three different variable.

Declaration of a Variable

Declaration of a variable is about telling a compiler about the existance of the variable. But in this case no memory is allocated for the variable.

Syntax for declaring a variable:
extern type variable_name;

Example:

extern int x;

In the above example we declared a variable named x of type integer. In this stage compiler will keep the record of the existance of variable x but will not allocate any memory space.

Defining a Variabe

For using any variable we need to define it first so that the compiler knows about the existance of it and allocate memory for it. If we are defining a variable then there is no need to declare it.

Syntax for Defining a variable:
type variable_name;

Example:

int ojhabikash;
float ojha;

Initializing a Variabe

If you want the variable to have some initial value then Initializing it is the best approach.

Syntax for Initializing a variable:
type variable_name = value;

Example:

int ojhabikash = 10;

Program example of variables in C

//An example of variables in c
#include<stdio.h>

int main()
{
    int length = 10, width = 5, area;  //declaration, definition and initialization
    
    area = length*width;  //assigning a value

    printf("Area is = %d \n", area);  //using of variable
    return 0;
}



Area is = 50