抽象类－编写一个程序，用于计算正方形、矩形、直角三角形和圆的面积之和。
源程序：
//纯虚函数与抽象类
#include <iostream>
using namespace std;
class shape //shape类中有纯虚函数，所以shape是抽象类，抽象类定义的对象也是抽象的，只能用指针对象，不能用普通对象，更不能用普通对象的实例化
{ //如在主函数中用 shape A(5)就是错误的，只能用 shape *pa;
public:
virtual double area() = 0; //抽象类至少有一个虚函数，而且至少有一个是纯虚函数。这个函数就是一个纯虚函数
virtual double area1() //这是一个虚函数，因为area1()的返回类型是double，所以必须要定义return 0;
{
return 0;
}
};
class square :public shape
{
protected:
double H;
public:
square(double i)
{
H = i;
}
double area()
{
return H * H;
}
};
class circle :public square
{
public:
circle(double r) :square(r)
{}
double area()
{
return H * H * 3.14159;
}
};
class triangle :public square
{
protected:
double W;
public:
triangle(double h, double w) :square(h)
{
W = w;
}
double area()
{
return H * W * 0.5;
}
};
class rectangle :public triangle
{
public:
rectangle(double h, double w) :triangle(h, w)
{}
double area()
{
return H * W;
}
};
double total(shape* s[], int n)
{
double sum = 0.0;
for (int i = 0; i < n; i++)
sum = sum + s[i]->area();
return sum;
}
int main()
{
// shape A(6); //不能给抽象的对象实例化
shape* s[5];
s[0] = new square(4);
s[1] = new triangle(3, 6);
s[2] = new rectangle(3, 6);
s[3] = new square(6);
s[4] = new circle(10);
for (int i = 0; i < 5; i++)
{
cout << "s[" << i << "]=" << s[i]->area() << endl;
}
double sum = total(s, 5);
cout << "The total area is:" << sum << endl;
system("pause");
return 1;
}
运行结果：
