C++ Constants

Constants are like a variable except that once defined, their value never changes during the program's execution. In this tutorial, you will learn about Constants in C++.

Table of Contents

What are Constants?

Constants refer to as fixed values; Unlike variables whose value can be changed, constants - as the name implies, do not change; They remain constant. A constant must be initialized when created, and new values cannot be assigned to it later.

  • Constants are also called literals.
  • Constants can be any of the data types.
  • It is considered best practice to define constants using only upper-case names.

Constant Definition in C++

There are two other different ways to define constants in C++. These are:

  • By using the const keyword
  • By using #define preprocessor

Constant Definition by Using const Keyword

Syntax:

const type constant_name;

Example:

#include <iostream>
using namespace std;

int main()
{
    const int SIDE = 50;
    int area;
    area = SIDE*SIDE;
    cout<<"The area of the square with side: " << SIDE <<" is: " << area << endl;
    system("PAUSE");
    return 0;
}

Program Output:

cplusplus-constants

It is also possible to put const either before or after the type.

int const SIDE = 50;

or

const int SIDE = 50;

Constant Definition by Using #define preprocessor

Syntax:

#define constant_name;

Example:

#include <iostream>
using namespace std;

#define VAL1 20   
#define VAL2  6
#define Newline '\n'

int main()
{
    int tot; 
    tot = VAL1 * VAL2;
    cout << tot;
    cout << Newline;
}