声明类Shape以及它的3个派生类：Circle、Square、Rectangle，用虚函数分别计算几种图形的面积、周长，编写程序，建立基类指针数组，每个指针均指向一个派生类对象，利用基类指针遍历元素对象，求取所有图形面积之和。请绘制UML类图。

  1 //Shape.h
  2 #ifndef _SHAPE_H_
  3 #define _SHAPE_H_
  4 
  5 class Shape
  6 {
  7 public:
  8     virtual double S()=0;
  9     virtual double C()=0;
 10 };
 11 #endif
 12 
 13 //Circle.h
 14 #include "Shape.h"
 15 
 16 class Circle:public Shape
 17 {
 18 public:
 19     Circle(double ir);
 20     double S();
 21     double C();
 22 private:
 23     double r;
 24 };
 25 
 26 //Circle.cpp
 27 #include "Circle.h"
 28 #include <iostream>
 29 #define PI 3.14
 30 
 31 using namespace std;
 32 
 33 Circle::Circle(double ir)
 34 {
 35     r=ir;
 36     cout<<"<construct a circle>"<<endl;
 37 }
 38 double Circle::S()
 39 {
 40     return (PI*r*r);
 41 }
 42 double Circle::C()
 43 {
 44     return (2*PI*r);
 45 }
 46 
 47 //Square.h
 48 #include "Shape.h"
 49 
 50 class Square:public Shape
 51 {
 52 public:
 53     Square(double ia);
 54     double S();
 55     double C();
 56 private:
 57     double a;
 58 };
 59 //Square.cpp
 60 #include "Square.h"
 61 #include <iostream>
 62 
 63 using namespace std;
 64 
 65 Square::Square(double ia)
 66 {
 67     a=ia;
 68     cout<<"<construct a square>"<<endl;
 69 }
 70 double Square::S()
 71 {
 72     return (a*a);
 73 }
 74 double Square::C()
 75 {
 76     return(4.0*a);
 77 }
 78 
 79 //Rectangle.h
 80 #include "Shape.h"
 81 
 82 class Rectangle:public Shape
 83 {
 84 public:
 85     Rectangle(double iw,double ih);
 86     double S();
 87     double C();
 88 private:
 89     double w;
 90     double h;
 91 };
 92 
 93 //Rectangle.cpp
 94 #include "Rectangle.h"
 95 #include <iostream>
 96 
 97 using namespace std;
 98 
 99 Rectangle::Rectangle(double iw,double ih)
100 {
101     w=iw;
102     h=ih;
103     cout<<"<construct a rectangle>"<<endl;
104 }
105 double Rectangle::S()
106 {
107     return (w*h);
108 }
109 double Rectangle::C()
110 {
111     return (2*(w+h));
112 }
113 
114 //main.cpp
115 #include <iostream>
116 #include "Circle.h"
117 #include "Square.h"
118 #include "Rectangle.h"
119 
120 using namespace std;
121 
122 int main()
123 {
124     int i=0;
125     double c,s;
126     double sum=0;
127 
128     Circle circle1(1);
129     Square square1(2);
130     Rectangle rectangle1(3,4);
131 
132     Shape * p[3];
133     p[0]=&circle1;
134     p[1]=&square1;
135     p[2]=&rectangle1;
136 
137     cout<<endl<<"Circle:"<<endl;
138     for(i=0;i<3;i++)
139     {
140         c=p[i]->C();
141         cout<<"c"<<i<<"="<<c<<endl;
142     }
143     cout<<endl<<"Square:"<<endl;
144     for(i=0;i<3;i++)
145     {
146         s=p[i]->S();
147         cout<<"s"<<i<<"="<<s<<endl;
148         sum+=s;
149     }
150     cout<<"total square="<<sum<<endl;
151     return 0;
152 }

1.error: redefinition of class Shape

使用宏定义防止头文件Shape.h被多次包含

#ifndef _SHAPE_H（有空格！否则unrecognized preprocessing directive：）

#define _SHAPE_H（有空格！）

class Shape {

    //......

};

#endif

1. 定义指针数组

类型 * p[n];