考试复习 | 易学教程

声明抽象基类Shape，由它派生出3个子类：Circle（圆形）、Rectangle（矩形）、Triangle（三角形），用一个函数printArea分别求出以上三者的面积，三个图形的数据在定义对象时给定。再设计一个函数sumArea，求出三个图形面积之和。要求用基类指针数组，使它的每一个元素指向一个派生类对象。

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#include <iostream>
#include <cmath>
using namespace std;

const double PI = acos(-1.0);

class Shape {
public:
    virtual double getArea() = 0;
};

class Circle : public Shape
{
private:
    double R;
public:
    Circle(double r = 0) : R(r) {};
    double getArea() {
        return PI * R * R;
    }
};

class Rectangle : public Shape
{
private:
    double len,high;
public:
    Rectangle(double l = 0, double h = 0) : len(l), high(h) {};
    double getArea() {
        return len * high;
    }
};

class Triangle : public Shape
{
private:
    double di,H;
public:
    Triangle(double l = 0, double h = 0) : di(l), H(h) {};
    double getArea() {
        return di * H / 2;
    }
};

template <class T>
void printArea(T sa) {
    cout << sa.getArea() << endl;
}

double sumArea(Shape** p,int x) {
    double sum = 0;
    for(int i = 0;i < x; i++) {
        sum += p[i]->getArea();
    }
    return sum;
}

int main() {
    Circle circle(12.6);
    Rectangle rectangle(4.5,8.4);
    Triangle triangle(4.5,8.4);
    cout<<"area of circle    =";   
    printArea(circle);           
    cout<<"area of rectangle =";   
    printArea(rectangle);      
    cout<<"area of triangle  =";
    printArea(triangle);
    Shape *pt[3] = {&circle,&rectangle,&triangle};
    cout << sumArea(pt,3) << endl;
    return 0;
}

来源：http://www.cnblogs.com/gray035/archive/2013/05/05/3061458.html

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circle

triangle