C++中派生类来求面积

写一个程序，定义抽象基类Shape,由它派生出3个派生类：Circle(圆)、Rectangle(矩形)、Triangle(三角形)，用一个函数printArea分别输出以上三者的面积，3个图形的数据在定义对象时给定。

答案：
#include <stdio.h>
#include <stdlib.h>

#include <iostream>

using namespace std;

const double pi = 3.1415926;

class Shape
{
        public:
                Shape()
                {
                }
                virtual ~Shape()
                {
                }
                virtual void printArea() = 0;
};

class Circle : public Shape
{
        public:
                Circle(double radiu)
                {
                        this->radiu = radiu;
                }
                void printArea()
                {
                        printf("面积是: %f\n", pi * radiu * radiu);
                }
        private:
                double radiu;
};

class Rectangle : public Shape
{
        public:
                Rectangle(double width, double height)
                {
                        this->width = width;
                        this->height = height;
                }
                void printArea()
                {
                        printf("面积是: %f\n", width * height);
                }
        private:
                double width;
                double height;
};

class Triangle : public Shape
{
        public:
                Triangle(double bottom, double height)
                {
                        this->bottom = bottom;
                        this->height = height;
                }
                void printArea()
                {
                        printf("面积是: %f\n", bottom * height/2);
                }
        private:
                double bottom;
                double height;
};

int main(int argc, char *argv[])
{
        Circle c((double)2);
        c.printArea();

        Rectangle r((double)1, (double)2);
        r.printArea();

        Triangle t((double)1, (double)2);
        t.printArea();

        return 0;
}
 class Shape
{
public:
Shape(void);
~Shape(void);
virtual void printArea() = 0;
};

 class Circle:Shape
 {
 public:
 Circle(double radiu) {this->radiu = radiu;}
 void printArea()
 {
 printf("面积是: %f", radiu);
 }
 private:
 double radiu;
 };

  class Rectangle:Shape
 {
 public:
 Rectangle(double width, double height) 
 {
 this->width = width;
 this->height = height;
 }
 void printArea()
 {
 printf("面积是: %f", width * height);
 }
 private:
 double width;
 double height;
 };

   class Triangle:Shape
 {
 public:
 Triangle(double bottom, double height) 
 {
 this->bottom = bottom;
 this->height = height;
 }
 void printArea()
 {
 printf("面积是: %f", bottom * height/2);
 }
 private:
 double bottom;
 double height;
 };

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