using System;
public class Graph
{
 protected double ParaVal;
 protected double pi = 3.1415926;
 public Graph ( double Para )
 {
 ParaVal = Para;
 }
 //定義虛方法：求面積
 public virtual double Area( )
 {
 return ParaVal;
 }
}
//圖形的子類正方形
public class Square : Graph
{
 public Square( double Para ) : base ( Para )
 {
 }
 //重載正方形求面積的方法
 public override double Area( )
 {
 return ParaVal * ParaVal;
 }
}
//圖形的子類等邊三角形
public class EqTriangle : Graph
{
 public EqTriangle( double Para ) : base ( Para )
 {
 }
 //重載等邊三角形求面積的方法
 public override double Area()
 {
 return ParaVal * ParaVal * Math.Sin( pi/3 ) / 2;
 }
}
//圖形的子類圓
public class Circle : Graph
{
 public Circle( double Para ) : base( Para )
 {
 }
 //重載圓求面積的方法
 public override double Area( )
 {
 return pi * ParaVal * ParaVal;
 }
}
class Test
{
 public static void Main( )
 {
 double Length = 6;

 Graph Init = new Graph( Length );
 Graph Squa = new Square( Length );
 Graph Tria = new EqTriangle( Length );
 Graph Circ = new Circle( Length );
 Console.WriteLine("原始圖形的面積是：\t{0}", Init.Area());
 Console.WriteLine("正方形的面積是：\t{0}", Squa.Area());
 Console.WriteLine("等邊三角形的面積是：\t{0}", Tria.Area());
 Console.WriteLine("圓形的面積是： \t{0}", Circ.Area());
 }
}