// A client of Point that instantiates three points and calculates
// the circumference of the implied triangle.

using System;

public class Application{

  public static void Main(){

    Point  p1 = PromptPoint("Enter first point"),
           p2 = PromptPoint("Enter second point"),
           p3 = PromptPoint("Enter third point");

    double p1p2Dist = p1.DistanceTo(p2),   
           p2p3Dist = p2.DistanceTo(p3),   
           p3p1Dist = p3.DistanceTo(p1);   

    double circumference = p1p2Dist + p2p3Dist + p3p1Dist;

    Console.WriteLine("Circumference: {0} {1} {2}: {3}", 
                       p1, p2, p3, circumference);
  }

  public static Point PromptPoint(string prompt){
    Console.WriteLine(prompt);
    double x = double.Parse(Console.ReadLine()),
           y = double.Parse(Console.ReadLine());
    return new Point(x,y, Point.PointRepresentation.Rectangular);
  }

}

 
 
 
 
 
 
 
 
 
 
 
 
 
Notice that DistanceTo is used as an instance 
method. The alternative static usage
PointExtensions.DistanceTo(pi, pj) is more heavy.