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interface Ishape
    {
        double GetArea();
    }
    public class Rectangle : Ishape
    {
        public double dblWidth;
        public double dblHeight;
        public Rectangle(double _dblWidth, double _dblHeight)
        {
            this.dblWidth = _dblWidth;
            this.dblHeight = _dblHeight;
        }
        public double GetArea()
        {
            return this.dblHeight * this.dblWidth;
        }
    }
    public class Triangle : Ishape
    {
        public double dblEdge1;
        public double dblEdge2;
        public double dblEdge3;
        public Triangle(double _dblEdge1, double _dblEdge2, double _dblEdge3)
        {
            this.dblEdge1 = _dblEdge1;
            this.dblEdge2 = _dblEdge2;
            this.dblEdge3 = _dblEdge3;
        }
        public double GetArea()
        {
            double p = (this.dblEdge1 + this.dblEdge2 + this.dblEdge3) / 2.0;
            double area = Math.Sqrt(p * (p - this.dblEdge1) * (p - this.dblEdge2) * (p - this.dblEdge3));
            return area;
        }
    }
    public class Circle : Ishape
    {
        public double dblRadius;
        public Circle(double _dblRadius)
        {
            this.dblRadius = _dblRadius;
        }
        public double GetArea()
        {
            return 3.1415926 * this.dblRadius * this.dblRadius;
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            Ishape s;
            s = new Rectangle(1, 2);
            Console.WriteLine("矩形面积为：{0}",s.GetArea());
            s = new Triangle(3,4,5);
            Console.WriteLine("三角形面积为:{0}",s.GetArea());
            s = new Circle(1);
            Console.WriteLine("圆形面积为:{0}", s.GetArea());
        }
    }