C++ Constant

                                  C++ Constant

Types And Uses

What is Constant ?

• As similar to variable constant are data storage location. 
• As the name implies constant's value do not change. 
• They remain constant throughout the program. 
• Unlike variable whose value can be changed anywhere in the program.

There are two types of constant in C++. They are as follows :

1) Literal Constant

float PI=3.14;

The value that is directly typed into the program is called literal constant.

Here 3.14 is called literal constant. You cannot assign a value to 3.14.

2) Symbolic Constant

Symbolic Constant are represented by name.

There are two ways to declare a symbolic constant. They are as follows :

1) By using processor directive #define.
This is old way of declaring constant. It has now became obsolete way.

2) By using keyword const.
This way is appropriate way to declare constant.

                                           Area Of Circle Program

#include <iostream>

#define PI 3.14

using std::cout;
using std::cin;
using std::endl;

int main ()
{
    int r;
    cout << "Find the area of circle." << endl;
    cout << "Enter radius : ";
    cin >> r;
    float area = PI * r * r;
    cout << "The area of circle of radius     " << r << " is "
    << area << endl;
    return 0;
}