C#源代码—三角形面积、圆的面积

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace _2
{
    public abstract class shape
    {
        private string mc;
        public shape(string s)
        {
            Mc = s;
        }
        public string Mc
        {
            get 
            {
                return mc;
            }
            set 
            {
                mc = value;
            }
        }
        public double Area()
        {
            return 1;
        }
        public abstract double area
        {
            get;
        }
        public override string ToString()
        {
            return Mc + "面积为：" + string.Format("{0:F2}", area);
        }
    }
    public class triangle : shape
    {
        private int a,b,c;
        public triangle(int a,int b,int c, string id)
            : base(id)
        {
            this.a = a;
            this.b = b;
            this.c = c;
        }
        public double Area()
        {
            double p,s;
            p = (a + b + c) / 2;
            s = Math.Sqrt(p*(p-a)*(p-b)*(p-c));
            return s;
        }
        public override double area
        {
          
            get 
            {
                return Math.Sqrt(((a + b + c) / 2) * (((a + b + c) / 2) - a) * (((a + b + c) / 2) - b) * (((a + b + c) / 2) - c));
            }
        }
    }
    public class circles : shape 
    {
        public double r;
        public circles(double r, string id)
            : base(id)
        {
            this.r = r;
        }
        public double Area()
        {
            double s;
            s = 2 * 3.14 * r;
            return s;
        }
        public override double area
        {
            get 
            {
                return 2 * 3.14 * r;
            }
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            triangle s1 = new triangle(3,4,5,"三角形");
            circles c1 = new circles(4,"圆");
            string result1, result2;
            result1 = s1.ToString();
            result2 = c1.ToString();
            Console.WriteLine("{0}\n{1}",result1,result2);
            Console.WriteLine("第二种实现方法：");
            Console.WriteLine("三角形面积为：{0}\n圆的面积为：{1}", s1.Area(),   c1.Area());
        }
    }
}