[开发工具]C# 类的接口，继承 和类的实例化 使用。

using System;
namespace test
{
    internal class Program
    {
        static void Main(string[] args)
        {
            CArea cArea = new CArea(3,4,5,6,7,8);
            Console.WriteLine(cArea.GetArea());
            Console.ReadKey();
        }
    }

    public class CArea
    {
        private double aa, bb, cc, width, height, radius;
        public CArea(double a,double b,double c,double w,double h, double r)
        { 
            aa = a;
            bb = b; 
            cc = c;
            width = w;
            height = h;
            radius = r;
        }
        public double GetArea()
        {
            CTriangle cTriangle=new CTriangle(aa,bb,cc);
            CRect cRect = new CRect(width,height);
            CCircle cCircle = new CCircle(radius);
            return cTriangle.GetData()+cRect.GetData()+cCircle.GetData();
        }
    }
    public interface Ishape
    {
        double Area();
        double GetData();
    }
    public class CTriangle : Ishape
    {
        private double aa,bb,cc;
        public CTriangle(double a, double b, double c)
        { 
            aa = a;bb = b;cc = c;
        }
        public double Area()
        {
            double p = (aa + bb + cc) / 2.0;
            double area;
            area = Math.Sqrt(p*(p-aa)*(p-bb)*(p-cc));    
            return area;
        }

        public double GetData()
        {
            return Area();
        }
    }

    public class CRect : Ishape
    {

        private double width,height;
        public CRect(double w, double h)
        { 
            width = w;height = h;
        }

        public double Area()
        {
            return width * height;
        }

        public double GetData()
        {
            return Area();
        }
    }
    public class CCircle : Ishape
    {
        private double radius;
        public CCircle(double r)
        { 
            radius = r;
        }
        public double Area()
        {
            return Math.PI * radius * radius;
        }

        public double GetData()
        {
            return Area();
        }
    }

}

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