C++多态基础性练习

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/*动态多态、虚函数
要求：
1.定义Shape类，成员函数：calcArea(),构造函数、析构函数
2.定义Rec类，成员函数：calArea(),构造函数、析构函数
数据成员：m_dWidth,m_dHeight
3.定义Circle类，成员函数：calArea(),构造函数、析构函数
数据成员：m_dR
*/
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思考：
1.不加同名函数前不加virtual关键字
Shape*shape1 = new Rect(3,5);
Shape *shape2 = new Circle(5);
shape1->calcArea();
shape2->calcArea();
运算结果：调用计算面积函数时，均调用的是父类的计算函数

2.加上virtauala关键字后，调用子类计算函数
代码：
//头文件

#include<iostream>#include<stdlib.h>#include<string>using namespace std;class Shape{public:    Shape();    ~Shape();    double calcArea();};class Circle:public Shape{public:    Circle(double r);    ~Circle();     double calcArea();protected:    double m_dR;};class Rect :public Shape{    public:        Rect(double width,double height);        ~Rect();         double calcArea();    protected:    double m_dWidth;    double m_dHeight;};

//定义部分：

#include"Mult.h"Shape::Shape(){    cout << "Shape()" << endl;}Shape::~Shape(){    cout << "~Shape()" << endl;}double Shape::calcArea(){    cout << " Shape->calcArea()" << endl;    return 0;}Circle::Circle(double r){    m_dR = r;    cout << "Circle()" << endl;}Circle::~Circle(){    cout << "~Circle()" << endl;}double Circle::calcArea(){    cout << "Circle->calcArea()" << endl;    return 3.14*m_dR*m_dR;}Rect::Rect(double width, double height){    m_dWidth = width;    m_dHeight = height;    cout << "Rect()" << endl;}Rect::~Rect(){    cout << "~Rect()" << endl;}double Rect::calcArea(){    cout << "Rect->calcArea()" << endl;    return m_dWidth*m_dHeight;}

//测试部分

#include"Mult.h"int main(void){    Shape*shape1 = new Rect(3,5);    Shape *shape2 = new Circle(5);    shape1->calcArea();    shape2->calcArea();    delete shape1;    shape1 = NULL;    delete shape2;    shape2 = NULL;    system("pause");    return 0;}

运算结果：