《C++ 面向对象程序设计（第2版） 谭浩强编》——课后习题之编程题——第3章

3.2 分析下面的程序...

#include <iostream>
using namespace std;
class Date
{
public:
    Date(int, int, int);
    Date(int, int);
    Date(int);
    Date();
    void display();
private:
    int month;
    int day;
    int year;
};
Date::Date(int m,int d,int y):month(m),day(d),year(y)
{ }
Date::Date(int m,int d):month(m),day(d)
{
    year = 2005;
}
Date::Date(int m):month(m)
{
    day = 1;
    year = 2005;
}
Date::Date()
{
    month = 1;
    day = 1;
    year = 2005;
}
void Date::display()
{
    cout<<month<<"/"<<day<<"/"<<year<<endl;
}
int main()
{
    Date d1(10,13,2005);
    Date d2(12,30);
    Date d3(10);
    Date d4;
    d1.display();
    d2.display();
    d3.display();
    d4.display();
    return 0;
}

运行结果：

10/13/2005
12/30/2005
10/1/2005
1/1/2005

3.3 改写如下：

#include <iostream>
using namespace std;
class Date
{
public:
    Date(int=1,int=1,int=2005);//带默认参数的构造函数
    void display();
private:
    int month;
    int day;
    int year;
};
Date::Date(int m,int d,int y):month(m),day(d),year(y)
{ }
void Date::display()
{
    cout<<month<<"/"<<day<<"/"<<year<<endl;
}
int main()
{
    Date d1(10,13,2005);//month =10 day = 13  year = 2005
    Date d2(12,30);//第三个个参数为默认值 month =12 day = 30  year = 2005
    Date d3(10);//后两个参数为默认值 month =10 day = 1  year = 2005
    Date d4;    //三个参数全为默认值 month =1 day = 1  year = 2005
    d1.display();
    d2.display();
    d3.display();
    d4.display();
    return 0;
}

运行结果：

同上

 3.4 建立一个对象数组，内放5个学生的数据（学号，成绩），用指针指向数组首元素，输出第1,3,5学生的数据。

#include<iostream>
#include<string>
using namespace std;
class Student
{
public:
    Student(string, double);//声明含参的构造函数
    void display();
private:
    string stuNumber;
    double score;
};
Student::Student(string num, double grade):stuNumber(num), score(grade) //定义构造函数
{
}
void Student::display()
{
    cout<<stuNumber<<":"<<score<<endl;
}
int main()
{
    Student stus[]=
    {
        Student("2019001",87),
        Student("2019002",90),
        Student("2019003",80),
        Student("2019004",97),
        Student("2019005",93),
    };
    Student *p1 = stus;
    p1->display();
    (p1+2)->display();
    (p1+4)->display();
    return 0;
}

运行结果：

3.5 建立一个对象数组，内放5个学生的数据（学号，成绩），用指向对象的指针做函数参数，在max函数中找出5个学生中成绩最高者，并输出其学号。

#include<iostream>
#include<string>
using namespace std;
class Student
{
public:
    Student(string, double);//声明含参的构造函数
    friend void max(Student *);//声明友元函数
private:
    string stuNumber;
    double score;
};
Student::Student(string num, double grade):stuNumber(num), score(grade) //定义构造函数
{
}
void max(Student *pt)
{
    double maxScore = pt->score;
    int flag = 0;
    for(int i = 0; i < 4; i++)
    {
        if(maxScore < (pt+i)->score)
        {
            maxScore = (pt+i)->score;  //将指向较大值的指针赋给指向maxScore指针
            flag = i;
        }
    }
    cout << "The highest score is: " << maxScore << endl;
    cout << "No." << (pt + flag)->stuNumber << endl;
}
int main()
{
    Student stus[]=
    {
        Student("2019001",87),
        Student("2019002",90),
        Student("2019003",80),
        Student("2019004",97),
        Student("2019005",93),
    };
    Student *p1 = stus;
    max(p1);
    return 0;
}

运行结果：

 3.6 分析程序

#include <iostream>
using namespace std;
class Student
{
public:
    Student(int n,float s):num(n),score(s) {}
    void change(int n,float s) {
        num=n;
        score=s;
    }
    void display()
    {
        cout<<num<<" "<<score<<endl;
    }
private:
    int num;
    float score;
};

int main()
{
    Student stud(101,78.5);
    stud.display();
    stud.change(101,80.5);
    stud.display();
    return 0;
}

 运行结果：

101 78.5
101 80.5

3.7 将第6题的程序分别作以下修改，分析所修改部分的含义以及编译和运行的情况。
(1) 将main函数第2行改为

const Student stud(101,78.5);

运行结果：编译错误

(2) 在(1)的基础上修改程序，使之能正常运行，用change函数修改数据成员num和score的值。

#include <iostream>
using namespace std;
class Student
{
public:
    Student(int n,float s):num(n),score(s) {}
    void change (int n,float s) const { num=n; score=s;}
    void display ()const
    {
        cout << num << " " << score << endl;
    }
private:
    mutable int num;
    mutable float score;
};

int main()
{
    const Student stud(101,78.5);
    stud.display();
    stud.change(101,80.5);
    stud.display();
    return 0;
}

(3) 将main函数改为
int main( )
{Student stud(101,78.5);
Student *p=&stud;
p->display( );
p->change(101,80.5);
p->display( );
return 0;
其他部分仍同第6题的程序。
(4) 在(3)的基础上将main函数第3行改为const Student *p=&stud;

#include <iostream>
using namespace std;
class Student
{
public:
    Student(int n,float s):num(n),score(s) {}
    void change (int n,float s) { num=n; score=s;}
    void display ()const
    {
        cout << num << " " << score << endl;
    }
private:
    int num;
    float score;
};

int main()
{
    Student stud(101,78.5);
    const Student *p=&stud;
    p->display();
    stud.change(101,80.5);
    p->display();
    return 0;
}

(5) 再把main函数第3行改为Student *const p=&stud;

 

#include <iostream>
using namespace std;
class Student
{
public:
    Student(int n,float s):num(n),score(s) {}
    void change (int n,float s) { num=n; score=s;}
    void display ()const
    {
        cout << num << " " << score << endl;
    }
private:
    int num;
    float score;
};

int main()
{
    Student stud(101,78.5);
    Student * const p=&stud;
    p->display();
    stud.change(101,80.5);
    p->display();
    return 0;
}