1、章 多态性与虚函数1.在例 12.1程序基础上作一些修改。定义 Point /Point.h#ifndef POINT_H#define POINT_H using namespace std;class Point;ostream y=b;void Point:setPoint(float a,float b)x=a;y=b;ostream float Circle:getRadius() const return radius;float Circle:area() constreturn float(3.14159*radius*radius);ostream float Cylinde
2、r:getHeight() const return height;float Cylinder:area() const return float(2*Circle:area()+2*3.14159*radius*height);float Cylinder:volume() constreturn Circle:area()*height;ostream cout把构造函数修改为带参数的函数，在建立对象时初始化。#include using namespace std;class Pointpublic:Point(double a,double b):x(a),y(b)Point()co
3、ut先不将析构函数声明为 virtual,在 main函数中另设一个指向 Circle类对象的指针变量.#include using namespace std;class Pointpublic:Point(double a,double b):x(a),y(b)Point()cout不作第（2）点的修改而将析构函数声明为 virtual,运行程序，分析结果#include using namespace std;class Pointpublic:Point(double a,double b):x(a),y(b)virtualPoint()coutusing namespace std;
4、class Shapepublic:virtual double area() const =0;class Circle:public Shapepublic:Circle(double r):radius(r) virtual double area() const return 3.14159*radius*radius;protected:double radius; ;class Rectangle:public Shapepublic:Rectangle(double w,double h):width(w),height(h) virtual double area() cons
5、t return width*height; protected:double width,height; ;class Triangle:public Shapepublic:Triangle(double w,double h):width(w),height(h)virtual double area() const return 0.5*width*height; protected:double width,height; ;void printArea(const Shape class Shapepublic:virtual double area() const =0; ;cl
6、ass Circle:public Shapepublic:Circle(double r):radius(r)virtual double area() const return 3.14159*radius*radius;protected:double radius; ;class Square:public Shapepublic:Square(double s):side(s) virtual double area() const return side*side; protected:double side;class Rectangle:public Shapepublic:R
7、ectangle(double w,double h):width(w),height(h) virtual double area() const return width*height; protected:double width,height; ;class Trapezoid:public Shapepublic:Trapezoid(double t,double b,double h):top(t),bottom(t),height(h)virtual double area() const return 0.5*(top+bottom)*height;protected:doub
8、le top,bottom,height;class Triangle:public Shapepublic: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); Trapezoid trapezoid(2.0,4.5,3.2);
9、Triangle triangle(4.5,8.4); Shape *pt5= double areas=0.0; for(int i=0;iarea();cout#include using namespace std;int main()double a,b,c,s,area;coutabc;if (a+b#include using namespace std;int main()float a5;coutai;coutusing namespace std;void main() int i,j,k;for(i=0;i#include using namespace std;void
10、fun1()int a10;ofstream outfile1(“f1.dat“),outfile2(“f2.dat“);if(!outfile1)cerrai;outfile1ai;outfile2a; outfileai; for(i=0;iaj+1)t=aj;aj=aj+1;aj+1=t;infile.close(); ofstream outfile(“f2.dat“,ios:out);if(!outfile)cerr#include using namespace std;struct staffint num;char name20;int age;double pay;int m
11、ain()staff staf7=2101,“Li“,34,1203,2104,“Wang“,23,674.5,2108,“Fun“,54,778,3006,“Xue“,45,476.5,5101,“Ling“,39,656.6,staf1;fstream iofile(“staff.dat“,ios:in|ios:out|ios:binary);if(!iofile)cerrstaf1.numstaf1.namestaf1.agestaf1.pay;iofile.seekp(0,ios:end);iofile.write(char *)iofile.seekg(0,ios:beg);for(
12、i=0;inum;while(num)find=false;iofile.seekg(0,ios:beg);for(i=0;inum;iofile.close();return 0;6.在例 13.17的基础上修改程序，将存放在 C数组中的数据读入并显示出来。#include #include using namespace std;struct studentint num;char name20;double score;int main()int i;student stud3=1001,“Li“,78,1002,“Wang“,89.5,1004,“Fun“,90,stud13;char
13、 c50;strstream strio(c,50,ios:in|ios:out);for(i=0;istud1i.numstud1i.namestud1i.score;cout#include #include using namespace std;struct studentint num;char name20;double score;int main()student stud3=1001,“Li“,78,1002,“Wang“,89.5,1004,“Fun“,90,stud13;char c50;int i;ostrstream strout(c,50);for(i=0;istud1i.numstud1i.namestud1i.score;cout“data from array c to array stud1:“endl;for(i=0;i3;i+)coutstud1i.num“ “stud1i.name“ “stud1i.scoreendl;coutendl;return 0;
