Defining Constants

Constants which are also called Literals are referred to as fixed or definite values in a program that may not alter. it can exist as any data type and can be divided into Floating-Point Numerals, Integer Numerals, Strings, Boolean Values, and Characters. However, they can be used the way regular variables are used in a program, except that their values cannot be modified after being defined. 

How to Define Constants in C++ Language?

• Using #define preprocessor
• Using const keyword 

The #define Preprocessor: 

The syntax below shows to use the #define preprocessor to define a constant. 

Syntax:

#define identifier value

Example:

#include <iostream.h>
#define PI 3.14
#define NEWLINE 'n'

int main()
{
    int radius = 10;
    float area;

    area = PI * radius * radius;  //area = PI r2
    cout << "Radius of Circle: " << radius;
    cout << NEWLINE;
    cout << "Area of Circle: " << area;
    return 0;
}

If you compiled and execute the code above, you will get the following result:

The const Keyword: 

The syntax below shows to use of the const prefix to define a constant.

Syntax:

const type variable = value;

Example:

#include <iostream.h>

int main()
{
    const float PI = 3.14;
    const char NEWLINE = 'n';
    int radius = 10;
    float area;

    area = PI * radius * radius;
    cout << "Radius of Circle: " << radius;
    cout << NEWLINE;
    cout << "Area of Circle: " << area;
    return 0;
}

If you compiled and execute the code above, you will get the following result: