using System;

public class Program

{

    public static void Main()

    {

        //creating instances of Circle class and invoking members of tht class

          Circle c1 = new Circle(5);

          float result1 = c1.CalculateArea();

          Console.WriteLine("Area={0}",result1);

​

​

           Circle c2 = new Circle(6);

           float result2 = c2.CalculateArea();

           Console.WriteLine("Area={0}",result2);

        Console.WriteLine(Circle.pi);//refering to static field

    }

}

​

class Circle

    {

        //members of this class

        public  static float pi;//static field

         int radius;//Instance field

​

         static Circle()

         {

            Console.WriteLine("static constructor");

            Circle.pi=3.141F; 

         }

         public Circle(int r)

         {

             Console.WriteLine("Instance constructor");

             this.radius = r;

         }

​

        public float CalculateArea()

        {

            return pi *this.radius * this.radius;

        }

​

    }

​