4.17~4.22

4.17

#include<iostream>using namespace std;class Student{public:void setstu(int num,float s){number=num;score=s;}    void disp(){cout<<number<<" "<<score<<endl;}private:int number;float score;};int main(){Student stu[6];Student*p;stu[0].setstu(11,90);    stu[1].setstu(12,90.5);stu[2].setstu(13,91);stu[3].setstu(14,92);stu[4].setstu(15,93);stu[5].setstu(16,89.5);p=stu;p=p+1;for(int i=1;i<=3;p=p+2,i++)    p->disp();return 0;}

4.18

#include <iostream>using namespace std;class Student {public:Student(int, float);void max(Student* s);private:int num;float score;};Student::Student(int n, float s):num(n),score(s){}void Student::max(Student* s){int i, max_num=0, max_score=0;for(i=0;i<6;++i)if((s+i)->score > max_score){max_score=(s+i)->score;max_num=(s+i)->num;}cout<<"所有学生中成绩最高学生的学号为:"<<max_num<< endl;}int main(){  int i;Student s[6]={Student(11,88),Student(12,91),Student(13,89),Student(14,92.5),Student(15,96),Student(16,92)};Student *p;p=&s[0];s[i].max(p);return 0;}

4.19

#include<iostream>using namespace std;class book{public:book(int i){qu=i;price=qu*10;}void disp(){cout<<"qu*price="<<qu*price<<endl;}private:int qu;float price;};int main(){int i;book b1[5]={1,2,3,4,5};for(i=0;i<5;i++){b1[i].disp();}return 0;}

4.20

#include<iostream>using namespace std;class book{public:void setbook(int i){qu=i;price=qu*10;}void disp(){cout<<"qu*price="<<qu*price<<endl;}private:int qu;float price;};int main(){  book b1[5];    book *p;    b1[0].setbook(1);    b1[1].setbook(2);    b1[2].setbook(3);    b1[3].setbook(4);    b1[4].setbook(5);p=b1;int i;    for(i=0;i<5;i++,p++)b1[4-i].disp();return 0;}

4.21

#include<iostream>#include<string>using namespace std;class Student{public:Student(string name1,int number1,float score1);    void show();void show_count_sum_ave();private:string name;int number;float score;static int count;static float sum;static float ave;};Student::Student(string name1,int number1,float score1){name=name1;number=number1;score=score1;count++;sum+=score;ave=sum/count;}void Student::show(){cout<<"name:"<<name<<endl;cout<<"number:"<<number<<endl;cout<<"score:"<<score<<endl;}void Student::show_count_sum_ave(){cout<<"count:"<<count<<endl;cout<<"sum:"<<sum<<endl;cout<<"ave:"<<ave<<endl;}int Student::count=0;float Student::sum=0.0;float Student::ave=0.0;int main(){Student stu1("Xiao",30,89);stu1.show();stu1.show_count_sum_ave();Student stu2("Yuan",33,91);stu2.show();stu2.show_count_sum_ave();Student stu3("Chen",2,82.5);stu3.show();stu3.show_count_sum_ave();return 0;}

4.22

#include <iostream>#include <cmath>using namespace std;class Point{public:    Point(float x1, float y1):x(x1),y(y1){}void showpoint(){cout << "(x,y)=(" <<x << "," << y << ")" << endl;}    friend float dist(Point &, Point &);private:    float x;    float y;};float dist(Point & A, Point & B){   return sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));}int main(){    Point a(1.2, 2);    Point b(1.4, 3);    a.showpoint();    b.showpoint();    cout << "a与b间的距离是：" << dist(a, b) <<endl;    return 0;}