using System;

// Here's a basic interface for geometric shapes.
public interface IGeometry
{
    double Area();
    double Perimeter();
}

// For our example we'll implement this interface on
// Rectangle and Circle types.
public class Rectangle : IGeometry
{
    public double Width { get; set; }
    public double Height { get; set; }

    // To implement an interface in C#, we just need to
    // implement all the methods in the interface.
    public double Area()
    {
        return Width * Height;
    }

    public double Perimeter()
    {
        return 2 * Width + 2 * Height;
    }
}

public class Circle : IGeometry
{
    public double Radius { get; set; }

    // The implementation for Circle.
    public double Area()
    {
        return Math.PI * Radius * Radius;
    }

    public double Perimeter()
    {
        return 2 * Math.PI * Radius;
    }
}

public class Program
{
    // If a parameter has an interface type, then we can call
    // methods that are in the named interface. Here's a
    // generic Measure method taking advantage of this
    // to work on any IGeometry.
    static void Measure(IGeometry g)
    {
        Console.WriteLine(g);
        Console.WriteLine(g.Area());
        Console.WriteLine(g.Perimeter());
    }

    public static void Main()
    {
        var r = new Rectangle { Width = 3, Height = 4 };
        var c = new Circle { Radius = 5 };

        // The Circle and Rectangle types both
        // implement the IGeometry interface so we can use
        // instances of these types as arguments to Measure.
        Measure(r);
        Measure(c);
    }
}