c++多态问题，如何进行最后的面积求和

问题遇到的现象和发生背景

求各种图形的面积，但不知道如何解决最后的所有图形面积相加的问题

问题相关代码，请勿粘贴截图

#include<iostream>
#define Pi 3.14159
using namespace std;
class CShape{
protected:
 double x,y;
public:
 void set(double i,double j)
 {
  x=i;
  y=j;
 }
 virtual double GetArea()=0;
};

class CRectangle:public CShape{
public:
 double GetArea(){
  return x*y; 
 }
};

class CCircle: public CShape
{ 
 private:
  double radius;
 public:
  CCircle(double r):radius(r){ }
        double GetArea() { return Pi*radius*radius;}  
};

class CSquare: public CShape{
private:
    double side;
public:
    CSquare(double s):side(s){ }
        double GetArea(){ return side*side;}
};

class CTrapezoid:public CShape{
private:
    double high,bottom,waist;
public:
    CTrapezoid(double h,double b,double w):high(h),bottom(b),waist(w){ };
        double GetArea(){ return 0.5*(high+bottom)*waist;}
};

class CTriangle:public CShape{
private:
    double length,width;
public:
    CTriangle(double le,double wi):length(le),width(wi){ };
        double GetArea(){ return 0.5*length*width;}
};
int main()
{
 double sum=0;
 CShape *c;
 CCircle i(6.6);
 CRectangle r;
 CSquare s(8);
 CTrapezoid z(1,2,3);
 CTriangle g(3,4);
 c=&r;
 c->set(6,6);
 cout<<"CRectangle area:"<<c->GetArea()<<endl;
 c=&i;
 cout<<"CCircle area:"<<c->GetArea()<<endl;
 c=&s;
 cout<<"CSquare area:"<<c->GetArea()<<endl;
 c=&z;
 cout<<"CTrapezoid area:"<<c->GetArea()<<endl;
 c=&g;
 cout<<"CTriangle area:"<<c->GetArea()<<endl;
 return 0;
}

运行结果及报错内容

我的解答思路和尝试过的方法

我想要达到的结果

最后输出一个图形面积之和的结果

```c++
int main()
{
 double sum=0;
 CShape *c;
 CCircle i(6.6);
 CRectangle r;
 CSquare s(8);
 CTrapezoid z(1,2,3);
 CTriangle g(3,4);
 c=&r;
 c->set(6,6);
 sum += c->GetArea();
 cout<<"CRectangle area:"<<c->GetArea()<<endl;
 c=&i;
 sum += c->GetArea();
 cout<<"CCircle area:"<<c->GetArea()<<endl;
 c=&s;
 sum += c->GetArea();
 cout<<"CSquare area:"<<c->GetArea()<<endl;
 c=&z;
 sum += c->GetArea();
 cout<<"CTrapezoid area:"<<c->GetArea()<<endl;
 c=&g;
 sum += c->GetArea();
 cout<<"CTriangle area:"<<c->GetArea()<<endl;
 cout<<"Total area:"<<sum<<endl;
 return 0;
}

```