In this article we will see a small example of using constants in c#. constants are declared with a keyword const .
The program below is to find the area and perimeter of circle in which we use const .
In the program below we have declared PI as a constant whose value is given as 3.14
It means PI value cannot be changed either at compile time or run-time .
Any Integral or string variables can be declared as constants.
We can also declare constants as public to use it in all the classes in a program.
using System;
namespace Constants
    class Program
        static void Main(string[] args)
            //declaring const variable PI
            constdouble PI = 3.14;
            Console.WriteLine(“*** ***”);
            Console.WriteLine(“>>> c# Program to find Area and Perimeter of Circle <<< n”);
            Console.Write(“Enter radius value: “);
            intr = Convert.ToInt32(Console.ReadLine()); //taking radius as input
            double area = PI * r * r; //getting area of circle
            Console.WriteLine(“Are of circle is: “ + area);
            //if we try to assign a value to PI , we get compile-time error
            //PI = 123;
            doubleperimeter = 2 * PI * r; //getting perimeter of circle
            Console.WriteLine(“Perimeter of circle: “ + perimeter);

Sample Output :

Constants C-Sharp Output