using System;

//structs are value types and should be immutable

​

public readonly struct Circle

{

  public double Radius {get;}

  public Circle(double radius)

  {

    Radius = radius;

  }

​

  public double GetArea()

  {

      return( Radius * Radius) * 3.14159265359

;

  }

}

​

class MainClass {

  public static void Main (string[] args) {

​

    Circle myCircle = new Circle(30);

    Console.WriteLine(myCircle.GetArea());

  }

}