请编写一个抽象类Shape，在此基础上派生出类Rectangle和类Circle，二者都有计算对象面积的函数getArea()和计算对象周长的函数getPerim()
为了避免精度问题，这里取圆周率 π=3 #include题目已处理，不必实现
样例输入 输出
3 4 5
12-14 75-30
#define PI 3
class Shape {
public:
virtual double getArea() = 0;
virtual double getPerim() = 0;
};
class Rectangle : public Shape {
double length;
double width;
public:
Rectangle() = default;
Rectangle(double l, double w) : length(l), width(w) {}
double getArea() {
return length * width;
}
double getPerim() {
return (length + width) * 2;
}
};
class Circle : public Shape {
double radius;
public:
Circle() = default;
Circle(double r):radius(r){}
double getArea() {
return PI*radius*radius;
}
double getPerim() {
return 2*PI*radius;
}
};
