C# Tutorial P20 - Static and instance class members

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using System;
class Circle
{
    float _PI = 3.14F;
    int _Radius;

    public Circle(int Radius)
    {
        this._Radius = Radius;
    }

    public float CalculateArea()
    {
        return this._PI * this._Radius * this._Radius;
    }
}

class Program
{
    public static void Main()
    {
        Circle C1 = new Circle(5);
        float Area = C1.CalculateArea();

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

        Circle C2 = new Circle(6);
        float Area = C2.CalculateArea();

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


using System;
class Circle
{
    public static float _PI;
    int _Radius;

    static Circle()
    {
        Console.WriteLine("Static Constructor called");
        Circle._PI = 3.14F;
    }

    public Circle(int Radius)
    {
        Console.WriteLine("Instance Constructor called");
        this._Radius = Radius;
    }

    public float CalculateArea()
    {
        return this._PI * this._Radius * this._Radius;
    }
}

class Program
{
    public static void Main()
    {
        //Circle C1 = new Circle(5);
        //float Area = C1.CalculateArea();

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

        //Circle C2 = new Circle(6);
        //float Area = C2.CalculateArea();
        
        //Console.WriteLine("Area = {0}", Area);

        Console.WriteLine(Circle._PI);
    }
}