继承与多态 相关问题 求解！

1）

#include 
using namespace std;
const double PI=3.14;
class Shape{
public:
double getArea()const;
double getPerimeter()const ;
};
double Shape::getArea()const{
return 0;
}
double Shape::getPerimeter()const{
return 0;
}
class Circle: public Shape{
public:
Circle(double r) : radius(r) {}
double getArea() const;
double getPerimeter() const;
private:
double radius;
};
double Circle::getArea( )const{
return PI*radius*radius;
}
double Circle::getPerimeter( )const{
return 2*PI*radius;
}
class Rectangle: public Shape{
public:
Rectangle( double w, double h): width(w), height(h) {}
double getArea()const;
double getPerimeter()const;
private:
double width;
double height;
};
double Rectangle::getArea()const{
return width*height;
}
double Rectangle::getPerimeter( )const{
return 2*(width+height);
}
int main(){
Shape *pShapes[3]; //定义基类指针数组
pShapes[0]=new Shape;
pShapes[1]=new Rectangle(3,4);
pShapes[2]=new Circle(1.0);
double totalArea=0, totalPerimeter=0;
for(int i=0;i<3;++i){
totalArea+=pShapes[i]->getArea();
totalPerimeter+=pShapes[i]->getPerimeter();
}
cout<<"Total Area: "<"Total Perimeter: "<for(int i=0;i<3;++i)
delete pShapes[i];
return 0;
}

2）修改 1)中的 Shape 类，将 getArea 和 getPerimeter 定义为虚函数，以实现多态
效果，并增加虚析构函数。重新运行程序，记录程序的运行效果。
3）修改 2)中的 Shape 类，将 getArea 和 getPerimeter 定义为纯虚函数，以实现多
态效果。修改主函数，重新运行程序，记录程序的运行效果。

class Shape{
public:
 
 
 
};
_double Shape::getArea()const{_
_return 0;_
}
_double Shape::getPerimeter()const{
return 0;_
}
int main(){
Shape *pShapes[3]; //定义基类指针数组
_pShapes[0]=new Shape;_
pShapes[0]=new Rectangle(3,4);
pShapes[1]=new Circle(1.0);
pShapes[2]=new Rectangle(2,1);
double totalArea=0, totalPerimeter=0;
for(int i=0;i<3;++i){
totalArea+=pShapes[i]->getArea();
totalPerimeter+=pShapes[i]->getPerimeter();
}
cout<<"Total Area: "<"Total Perimeter: "<for(int i=0;i<3;++i)
delete pShapes[i];
return 0;
}
运行结果：

4. 从 Shape 派生得到 Triangle 类（三角形类），在其中定义 3 个边长数据成员，
   实现构造函数和虚函数 getArea 和 getPerimeter。类的定义如下：

class Triangle : public Shape{
public:
Triangle(double newA, double newB, double newC);
virtual double getArea( )const;
virtual double getPerimeter( )const;
private:
double a, b, c;
};

【提示】计算三角形面积，可以参考海伦公式。调用 sqrt 函数时需要包含头
文件：#include
测试主程序修改如下。

int main(){
Shape *pShapes[3]; //定义基类指针数组
pShapes[0]=new Rectangle(3,4);
pShapes[1]=new Circle(1.0);
pShapes[2]=new Triangle(3,4,5);
double totalArea=0, totalPerimeter=0;
for(int i=0;i<3;++i){
totalArea+=pShapes[i]->getArea();
totalPerimeter+=pShapes[i]->getPerimeter();
}
cout<<"Total Area: "<"Total Perimeter: "<for(int i=0;i<3;++i)
delete pShapes[i];
}

（2）
#include <iostream>
using namespace std;
const double PI = 3.14;
class Shape {
public:
    virtual double getArea() const {
        return 0;
    }
    virtual double getPerimeter() const {
        return 0;
    }
    virtual ~Shape() {}
};
class Circle : public Shape {
public:
    Circle(double r) : radius(r) {}
    double getArea() const override {
        return PI * radius * radius;
    }
    double getPerimeter() const override {
        return 2 * PI * radius;
    }
private:
    double radius;
};
class Rectangle : public Shape {
public:
    Rectangle(double w, double h) : width(w), height(h) {}
    double getArea() const override {
        return width * height;
    }
    double getPerimeter() const override {
        return 2 * (width + height);
    }
private:
    double width;
    double height;
};
int main() {
    Shape* pShapes[3];
    pShapes[0] = new Shape;
    pShapes[1] = new Rectangle(3, 4);
    pShapes[2] = new Circle(1.0);
    double totalArea = 0, totalPerimeter = 0;
    for (int i = 0; i < 3; ++i) {
        totalArea += pShapes[i]->getArea();
        totalPerimeter += pShapes[i]->getPerimeter();
    }
    cout << "Total Area: " << totalArea << endl;
    cout << "Total Perimeter: " << totalPerimeter << endl;
    for (int i = 0; i < 3; ++i)
        delete pShapes[i];
    return 0;
}
（3）
#include <iostream>
using namespace std;
const double PI = 3.14;
class Shape {
public:
    virtual double getArea() const = 0;
    virtual double getPerimeter() const = 0;
    virtual ~Shape() {}
};
class Circle : public Shape {
public:
    Circle(double r) : radius(r) {}
    double getArea() const override {
        return PI * radius * radius;
    }
    double getPerimeter() const override {
        return 2 * PI * radius;
    }
private:
    double radius;
};
class Rectangle : public Shape {
public:
    Rectangle(double w, double h) : width(w), height(h) {}
    double getArea() const override {
        return width * height;
    }
    double getPerimeter() const override {
        return 2 * (width + height);
    }
private:
    double width;
    double height;
};
int main() {
    Shape* pShapes[3];
    pShapes[0] = new Rectangle(3, 4);
    pShapes[1] = new Circle(1.0);
    double totalArea = 0, totalPerimeter = 0;
    for (int i = 0; i < 2; ++i) {
        totalArea += pShapes[i]->getArea();
        totalPerimeter += pShapes[i]->getPerimeter();
    }
    cout << "Total Area: " << totalArea << endl;
    cout << "Total Perimeter: " << totalPerimeter << endl;
    for (int i = 0; i < 2; ++i)
        delete pShapes[i];
    return 0;
}