设计一个Shape接口和它的两个实现类Square和Circle 要求：Shape接口中有一个抽象方法area()，

#includeusing namespace std;class Shape{public: virtual double Area(double length){}};class Square:Shape{public: double Area(double length){coutArea( length )<<endl;}int main(){ Square s; Circle c; //边长为2的正方形面积