面积计算，为什么这段程序输出是空白(语言-c++)

Question

#include<bits/stdc++.h>
using namespace std;
class Shape{
    public:
    virtual    double Area();
    protected:
        double area;
};
class Circle:public Shape{
    public:
        Circle(int a);
        double Area();
    protected:
        int radius;
        double PI=3.14159;
       
        
};
class Rectangle:public Shape{
    public:
        Rectangle(int width1,int height1);
        double Area();
    protected:
        int width;
        int height;
};
double Shape::Area(){return area;}
Circle::Circle(int a){
    radius=a;
}
double Circle::Area(){
     area=PI*radius*radius;
}
Rectangle::Rectangle(int width1,int height1){
    width=width1;
    height=height1;
}
double Rectangle::Area(){
     area=width*height;
}
int main(){
    
    Shape *p[4];
    p[0]=new Circle(1);
    p[1]=new Circle(2);
    p[2]=new Rectangle(1,2);
    p[3]=new Rectangle(3,4);
    for(int i=0;i++;i<4){
        cout<<p[i]->Area()<<endl;
    }
    delete p;
    
}

样例输出
3.14
12.56
2
12

Answer 1

new 和 delete得成对使用
另外p是一个数组，如果你使用Shape *p = new Shape[4];的形式创建了对象
那么你必须使用delete [] p; 释放空间

int main() {

    Shape *p[4];
    p[0] = new Circle(1);
    p[1] = new Circle(2);
    p[2] = new Rectangle(1, 2);
    p[3] = new Rectangle(3, 4);
    for (int i = 0; i < 4; i++ ) {
        cout << p[i]->Area() << endl;
    }
    delete p[0];
    delete p[1];
    delete p[2];
    delete p[3];
    return 0;
}