编写程序：定义抽象基类Shape，由它派生出五个派生类

第1题

编写程序：定义抽象基类Shape，由它派生出五个派生类：Circle（圆形）、Square（正方形）、Rectangle（长方形）、Trapezoid（梯形）和Triangle（三角形），用虚函数分别计算各种图形的面积，并求出它们的和。要求用基类指针数组。使它的每一个元素指向一个派生类的对象。

注：主函数中定义如下对象

Circle circle(12.6);

Square square(3.5);

Rectangle rectangle(4.5,8.4);

Trapezoid trapezoid(2.0,4.5,3.2);

Triangle triangle(4.5,8.4);

 参考答案：

#include <iostream>
using namespace std;
class Shape
{public:
virtual double area() const =0;
};
 
class Circle:public Shape
{public:
Circle(double r):radius(r){}
virtual double area() const {return 3.14159*radius*radius;};
protected:
double radius;
};
 
class Square:public Shape
{public:
Square(double s):side(s){}
virtual double area() const {return side*side;}
protected:
double side;
};
 
class Rectangle:public Shape
{public:
Rectangle(double w,double h):width(w),height(h){}
virtual double area() const {return width*height;}
protected:
double width,height;
};
 
class Trapezoid:public Shape
{public:
Trapezoid(double t,double b,double h):top(t),bottom(t),height(h){}
virtual double area() const {return 0.5*(top+bottom)*height;}
protected:
double top,bottom,height;
};
 
class Triangle:public Shape
{public:
Triangle(double w,double h):width(w),height(h){}
virtual double area() const {return 0.5*width*height;}
protected:
double width,height;
};
 
int main()
{
Circle circle(12.6);
Square square(3.5);
Rectangle rectangle(4.5,8.4);
Trapezoidtrapezoid(2.0,4.5,3.2);
Triangle triangle(4.5,8.4);
Shape *pt[5]={&circle,&square,&rectangle,&trapezoid,&triangle};
double areas=0.0;
for(int i=0;i<5;i++)
{
areas=areas+pt[i]->area();
}
cout<<"totol of all areas="<<areas<<endl;
return 0;
}