Variables and Constants in C – C Programming Basics

Variables and constants in C or c++ are the two important concepts in the C Programming Basics. Let us define these one by one.

What are Variables ?

A variable refers to a storage area whose contents vary during processing.

For example, to store salary of a employee, we need a variable.

Declaration of C++ Variables –

A variable name is declared by

data_type variable_name;

where data_type is the data types provided by C++
and variable_name is the identifier. Thus, the naming convention rules for naming an identifier is also applicable to name of the variable.

To store salary of an employee,

int emp_salary;

if more than one variable is to be defined, then variable name is separated by commas.

int day, month, year;

Symbolic Variables – 

The variables are referred as symbolic variables as they are named locations or it can be said that we give a name to a location in the computer memory.

There are 2 values associated with a symbolic variable –

  • rvalue (pronounced as r-value) – data value of variable stored at some location
  • lvalue (pronounced as el-value) – location value of a variable, the memory address at which its data value is stored

variables and constants in C++

 

lvalue of emp_salary = 1001                lvalue of character = 1006
rvalue of emp_salary = 20000               rvalue of character = d

Initialization of Variables : Static Initialization and Dynamic Initialization

If we do not give the data value of variable, then the variable is called uninitialized variable. and the variable data valuse is said to be undefined.

Static Initialization – 

A variable is initialized by declaring/assigning its rvalue. C++ supports two forms of variable initialization at the time of variable definition :

int val = 100;  (or)
int val(100) ;

Dynamic Initialization (or) Run Time Initialization – 

If the initialization of variable is done at run time, it is called dynamic initialization. A variable can be initialized at run time using expressions at the place of declaration. For instance,

float avg = sum/count ;

What are C Constants or ‘const’ in C-

As said earlier, a constant never change their value during a program run.

Access Type : Read only.

How to create a C constant?

const keyword is required to create a constant. For example

const int c=100 ;   (or)
const c=100 ;

If the data type is not declared in initialization of constant, then automatically it is said to be an integer constant.

Difference Between Variables and Constants in c++

Basis Variables Constants
Definition A variable is a named location, whose value changes during a program run A constant is a named location, whose value never changes during a program run.
Syntax data_type variable_name const data_type variable_name= value
Example int a; const int a=100;
Static Initialization Variables can be initialize after its declaration also. constants must be initialized at the time of decelaration only.
Dynamic Initialization Variables can be initialize dynamically Dynamic Initialization of constant is not possible.

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