#include<iostream> using namespace std; class Rectangle { public: double width; double height; double area() { return width*height; } }; int main() { Rectangle rect1; Rectangle *p; p->width=1.2; cin>>p->height; cout<<p->area(); }

这段代码存在一个问题，即指针p没有被初始化，所以无法访问它所指向的对象。应该先将p指向一个已经存在的Rectangle对象，例如：

Rectangle rect1;
Rectangle *p = &rect1;
p->width=1.2;
cin>>p->height;
cout<<p->area();

这样就能正确地计算并输出矩形的面积了。

相关问题

编写以下代码#include <iostream> #include <iomanip> #include <cmath> using namespace std; class area_c1{ protected: double height; double width; public: area_c1(double r, double s){ height = r; width = s; } //定义纯虚函数area/使得类area_c1成为抽象类 @-@ }; //定义类rectangle，构造函数和成员函数area //area=height * width @-@ //定义类isosceles，构造函数和成员函数area //area=(height * width)/2 @-@ int main(){ double r1,s1; double r2,s2; cin>>r1>>s1; rectangle r(r1, s1); cin>>r2>>s2; isosceles i(r2, s2); //定义指针基类a @-@ a = &r; cout<< "The area of rectangle:" <<fixed<<setprecision(4)<< a->area() << endl; a = &i; cout << "The area of isosceles:" <<fixed<<setprecision(4)<< a->area() <<endl; return 0; }

这段代码存在问题，因为在类area_c1中定义了纯虚函数area，使得类area_c1成为抽象类，但是没有定义子类rectangle和isosceles中的area函数，导致编译会报错。

另外，在main函数中定义指针a时，需要先定义a的类型，即指向哪个类的指针，否则也会报错。

以下是修改后的代码：

#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

class area_c1{
protected:
double height;
double width;
public:
area_c1(double r, double s){
height = r;
width = s;
}
virtual double area()=0; //定义纯虚函数area/使得类area_c1成为抽象类
};

class rectangle: public area_c1{ //定义类rectangle，构造函数和成员函数area
public:
rectangle(double r, double s): area_c1(r, s){}
double area(){
return height * width;
}
};

class isosceles: public area_c1{ //定义类isosceles，构造函数和成员函数area
public:
isosceles(double r, double s): area_c1(r, s){}
double area(){
return (height * width) / 2;
}
};

int main(){
double r1,s1;
double r2,s2;
area_c1 *a; //定义指针基类a
cin>>r1>>s1;
rectangle r(r1, s1);
cin>>r2>>s2;
isosceles i(r2, s2);
a = &r;
cout<< "The area of rectangle:" <<fixed<<setprecision(4)<< a->area() << endl;
a = &i;
cout << "The area of isosceles:" <<fixed<<setprecision(4)<< a->area() <<endl;
return 0;
}

#include <iostream> #include <cmath> using namespace std; class figure { protected: double He; double Wi; public: figure(double H, double W); }; figure::figure(double H, double W) { cin >> W >> H; cout << W << " ### " << H << endl; He = H; Wi = W; } class rectangle :public figure { public: rectangle(double H, double W) :figure(H, W) { }; void area(); void display(); }; void rectangle::display() { cout << "W: " << Wi << "H: " << He << endl; } void rectangle::area() { cout << "S= " << Wi * He << endl; } class triangle :public figure { public: triangle(double H, double W) :figure(H, W) { }; void area(); void display(); }; void triangle::display() { cout << "W: " << Wi << "H: " << He << endl; } void triangle::area() { double n = 0.5; cout << n * Wi * He << endl; } int main() { double width, height; cin >> width >> height; triangle tri(width, height); rectangle rect(width, height); tri.display(); cout << ". The area is "; cout << tri.area() << endl; rect.display(); cout << ". The area is " << rect.area() << endl; return 0; }

这段代码中存在一些问题。具体问题如下：

1. `#include` 库文件时应该每个文件一行，而不是写在同一行。
2. 类 `figure` 的构造函数中的输入语句应该放在 `main` 函数中，而不是在构造函数中。
3. 类 `triangle` 和类 `rectangle` 中的 `area` 函数应该返回一个值，而不是 `void` 类型。
4. 在 `main` 函数中，输出 `tri.area()` 和 `rect.area()` 的语句应该分别放在 `tri.area()` 和 `rect.area()` 的函数调用后面。

下面是修改后的代码：

#include <iostream> 
#include <cmath>  

using namespace std;  

class figure { 
protected: 	
    double He; 	
    double Wi; 
public: 	
    figure(double H, double W) : He(H), Wi(W) {} 
}; 

class rectangle : public figure { 
public: 	
    rectangle(double H, double W) : figure(H, W) {} 	
    double area(); 	
    void display(); 
}; 

void rectangle::display() { 	
    cout << "W: " << Wi << "H: " << He << endl; 
} 

double rectangle::area() { 	
    return Wi * He; 
} 

class triangle : public figure {  
public: 	
    triangle(double H, double W) : figure(H, W) {}  	
    double area(); 	
    void display(); 
}; 

void triangle::display() { 	
    cout << "W: " << Wi << "H: " << He << endl; 
} 

double triangle::area() { 	
    double n = 0.5; 	
    return n * Wi * He; 
} 

int main() { 	
    double width, height; 	
    cin >> width >> height; 

    triangle tri(height, width); 	
    rectangle rect(height, width); 	

    tri.display(); 	
    cout << ". The area is " << tri.area() << endl; 
    rect.display(); 	
    cout << ". The area is " << rect.area() << endl; 

    return 0; 
}