C++计算圆形、矩形和三角形的面积

#include<iostream>
#include<iomanip> 
#define PI 3.1415926
using namespace std;
class Shape {
    public:
        virtual double printArea()=0;
};
class Circle:public Shape {
    private:
        double r;
    public:
        Circle(double x) {
            r=x;
        }
        virtual double printArea() {
            return PI*r*r;
        }
};
class Rectangle:public Shape {
    private:
        double w,h;
    public:
        Rectangle(double x,double y) {
            w=x,h=y;
        }
        virtual double printArea() {
            return w*h;
        }
};
class Triangle:public Shape {
    private:
        double w,h;
    public:
        Triangle(double x,double y) {
            w=x,h=y;
        }
        virtual double printArea() {
            return w*h/2;
        }
};
double printArea(Shape &x) {
	return x.printArea();
}
int main() {
    double a,b,c,d,e;
    cin>>a>>b>>c>>d>>e;
    Circle cir(a);
    Rectangle rec(b,c);
    Triangle tri(d,e);
    cout<<fixed<<setprecision(2)<<"area of circle="<<printArea(cir)<<'\n';
    cout<<fixed<<setprecision(2)<<"area of rectangle="<<printArea(rec)<<'\n';
    cout<<fixed<<setprecision(2)<<"area of triangle="<<printArea(tri)<<'\n';
    return 0;
}