《C++ primerplus》第13章练习题

 

1.对CD类的派生练习。基类CD类存储作者和作品号等信息，派生类Classic额外增加一格“主要作品”的信息。主函数使用拷贝构造函数、按引用传递参数的函数和指针来测试基类和派生类的功能。

注意继承类和基类的权限关系、初始化成员列表的使用。

class.h

#ifndef _CLASS_H_
#define _CLASS_H_

#include <iostream>
using std::cin;
using std::cout;

class CD
{
private:
    char performers[20] = {};    //初始化为空，不然输出一堆烫
    char label[20] = {};
    int selections;
    double playtime;

public:
    CD(const char *s1, const char*s2, int n, double x);    //自定义构造函数
    CD(const CD & d);    //拷贝构造函数
    CD();    //默认构造函数
    virtual ~CD();
    virtual void Report()const;
    virtual CD & operator = (const CD & d);

};

class Classic :public CD
{
private:
    char collection[50] = {};

public:
    Classic(const char *c, const char *s1, const char*s2, int n, double x);
    Classic();
    ~Classic();
    void Report()const;
    Classic & operator = (const Classic & d);
};

#endif

DefineClass.cpp

#include "class.h"

CD::CD(const char *s1, const char*s2, int n, double x)
{
    for (int i = 0; s1[i] != ''; i++)
    {
        performers[i] = s1[i];
    }
    for (int i = 0; s2[i] != ''; i++)
    {
        label[i] = s2[i];
    }
    selections = n;
    playtime = x;
}

CD::CD(const CD & d)
{
    for (int i = 0; d.performers[i] != ''; i++)
    {
        performers[i] = d.performers[i];
    }
    for (int i = 0; d.label[i] != ''; i++)
    {
        label[i] = d.label[i];
    }
    selections = d.selections;
    playtime = d.playtime;
}

CD::CD()
{

}

CD::~CD()
{

}

void CD::Report()const
{
    cout << "Performers: ";
    for (int i = 0; performers[i] != ''; i++)
    {
        cout << performers[i];
    }
    cout << "
";
    cout << "Label: ";
    for (int i = 0; label[i] != ''; i++)
    {
        cout << label[i];
    }
    cout << "
";
    cout << "Selections: " << selections << "
";
    cout << "Playtime: " << playtime << "
";
}

CD & CD::operator=(const CD & d)
{
    for (int i = 0; d.performers[i] != ''; i++)
    {
        performers[i] = d.performers[i];
    }
    for (int i = 0; d.label[i] != ''; i++)
    {
        label[i] = d.label[i];
    }
    selections = d.selections;
    playtime = d.playtime;

    return *this;
}

//derived class

Classic::Classic(const char *c, const char *s1, const char*s2, int n, double x):CD(s1,s2,n,x)
{
    for (int i = 0; c[i] != ''; i++)
    {
        collection[i] = c[i];
    }
}

Classic::Classic()
{

}

Classic::~Classic()
{

}

void Classic::Report()const 
{
    CD::Report();
    cout << "Collection: ";
    for (int i = 0; collection[i] != ''; i++)
    {
        cout << collection[i];
    }
    cout << "

";
}

Classic & Classic::operator = (const Classic & d)
{
    CD::operator=(d);
    for (int i = 0; d.collection[i] != ''; i++)
    {
        collection[i] = d.collection[i];
    }
    return *this;
}

main.cpp

#include "class.h"

void Bravo(const CD & disk);

int main()
{
    CD c1("Beatles", "Capitol", 14, 35.5);
    Classic c2 = Classic("Piano Sonata in B flat, Fantasia in C", "Alfred Brendel", "Philips", 2, 57.17);

    CD *pcd = &c1;

    cout << "Using Object directly:
";
    c1.Report();
    c2.Report();

    cout << "Using type cd * pointer to objects:
";
    pcd->Report();
    pcd = &c2;
    pcd->Report();

    cout << "Calling a function with a cd reference argument:
";
    Bravo(c1);
    Bravo(c2);

    cout << "Testing assignment:
";
    Classic copy;
    copy = c2;
    copy.Report();

    //pause
    cin.get();
    return 0;

}

void Bravo(const CD & disk)
{
    disk.Report();
}

2.以上题为基础。存储的字符数组用使用动态分配内存。

我初始化对象的时候把两个字符成员都设为了空指针，做题的过程中，了解到了空指针不能被赋值。其它需要注意的地方见注释。

ClassCD.h

#ifndef _CLASSCD_
#define _CLASSCD_

#include <iostream>

using std::cout;
using std::cin;

//Base Class Declare
class CD
{
private:
    char *performers = nullptr;
    char *label = nullptr;
    int selections;
    double playtime;

public:
    CD(const char *s1, const char*s2, int n, double x);    //自定义构造函数
    CD(const CD & d);    //拷贝构造函数
    CD();    //默认构造函数
    virtual ~CD();
    virtual void Report()const;
    virtual CD & operator = (const CD & d);
};

//Base Class Define
CD::CD(const char *s1, const char*s2, int n, double x)
{
    //根据s1和s2的长度分配内存
    //strlen()计算的长度不包含终止符''
    //为了不影响report()的执行，分配的内存长度+1，使其包含''
    performers = new char[strlen(s1)+1];
    for (int i = 0; i < (strlen(s1)+1); i++)
    {
        performers[i] = s1[i];
    }

    label = new char[strlen(s2)+1];
    for (int i = 0; i < (strlen(s2)+1); i++)
    {
        label[i] = s2[i];
    }

    selections = n;
    playtime = x;
}

CD::CD()
{
    selections = 0;
    playtime = 0;
}

CD::CD(const CD & d)
{
    int count;

    //对象分配内存的成员不是空指针才会赋值，防止内存访问混乱
    if (d.performers != nullptr)
    {
        //获取等号右边的类里面分配的长度
        for (count = 0; d.performers[count] != ''; count++)
        {
            ;
        }

        //根据它的长度来分配自身的长度，加上''一位
        performers = new char[count + 1];

        //给自身成员变量赋值，取到终止符后停止
        for (int i = 0; d.performers[i] != ''; i++)
        {
            performers[i] = d.performers[i];
            if (d.performers[i + 1] == '')
            {
                performers[i + 1] = '';
                break;
            }
        }
    }

    //以下同理
    if (d.label != nullptr)
    {
        for (count = 0; d.label[count] != ''; count++)
        {
            ;
        }

        label = new char[count + 1];

        for (int i = 0; d.label[i] != ''; i++)
        {
            label[i] = d.label[i];
            if (d.label[i + 1] == '')
            {
                label[i + 1] = '';
                break;
            }
        }
    }
    
    selections = d.selections;
    playtime = d.playtime;
}

CD::~CD()
{
    //是空指针，说明从未分配过内存，不需要释放
    //不是空指针，说明分配了内存，需要释放
    if (performers != nullptr)
    {
        delete[] performers;
    }
    if (label != nullptr)
    {
        delete[] label;
    }
}

void CD::Report()const
{
    //对象分配内存的成员不是空指针才会打印，防止内存访问混乱
    cout << "Performers: ";
    if (performers != nullptr)
    {
        for (int i = 0; performers[i] != ''; i++)
        {
            cout << performers[i];
        }
    }
    cout << "
";

    cout << "Label: ";
    if (label != nullptr)
    {
        for (int i = 0; label[i] != ''; i++)
        {
            cout << label[i];
        }
    }
    cout << "
";

    cout << "Selections: " << selections << "
";
    cout << "Playtime: " << playtime << "
";
}

CD & CD::operator=(const CD & d)
{
    int count;

    //对象分配内存的成员不是空指针才会赋值，防止内存访问混乱
    if (d.performers != nullptr)
    {
        //获取等号右边的类里面分配的长度
        for (count = 0; d.performers[count] != ''; count++)
        {
            ;
        }

        //根据它的长度来分配自身的长度，加上''一位
        performers = new char[count + 1];

        //给自身成员变量赋值，取到终止符后停止
        for (int i = 0; d.performers[i] != ''; i++)
        {
            performers[i] = d.performers[i];
            if (d.performers[i + 1] == '')
            {
                performers[i + 1] = '';
                break;
            }
        }
    }

    //以下同理
    if (d.label != nullptr)
    {
        for (count = 0; d.label[count] != ''; count++)
        {
            ;
        }

        label = new char[count + 1];

        for (int i = 0; d.label[i] != ''; i++)
        {
            label[i] = d.label[i];
            if (d.label[i + 1] == '')
            {
                label[i + 1] = '';
                break;
            }
        }
    }
    
    selections = d.selections;
    playtime = d.playtime;

    return *this;
}

//Derived Class Declare
class Classic :public CD
{
private:
    char *collection = nullptr;

public:
    Classic(const char *c, const char *s1, const char*s2, int n, double x);
    Classic();
    ~Classic();
    void Report()const;
    Classic & operator = (const Classic & d);
};

//Derived Class Define
Classic::Classic(const char *c, const char *s1, const char*s2, int n, double x) :CD(s1, s2, n, x)
{
    collection = new char[strlen(c) + 1];
    for (int i = 0; i < (strlen(c) + 1); i++)
    {
        collection[i] = c[i];
    }
}

Classic::Classic()
{
    
}

Classic::~Classic()
{
    if (collection != nullptr)
    {
        delete[] collection;
    }
}

void Classic::Report()const
{
    CD::Report();
    cout << "Collection: ";
    if (collection != nullptr)
    {
        for (int i = 0; collection[i] != ''; i++)
        {
            cout << collection[i];
        }
    }
    cout << "

";
}

Classic & Classic::operator = (const Classic & d)
{
    CD::operator=(d);
    int count;

    if (d.collection != nullptr)
    {
        for (count = 0; d.collection[count] != ''; count++)
        {
            ;
        }

        collection = new char[count + 1];

        for (int i = 0; d.collection[i] != ''; i++)
        {
            collection[i] = d.collection[i];
            if (d.collection[i + 1] == '')
            {
                collection[i + 1] = '';
                break;
            }
        }
    }

    return *this;
}


#endif

main.cpp

#include "ClassCD.h"

void Bravo(const CD & disk);

int main()
{
    CD c1("Beatles", "Capitol", 14, 35.5);
    Classic c2 = Classic("Piano Sonata in B flat, Fantasia in C", "Alfred Brendel", "Philips", 2, 57.17);

    CD *pcd = &c1;

    cout << "Using Object directly:
";
    c1.Report();
    c2.Report();

    cout << "Using type cd * pointer to objects:
";
    pcd->Report();
    pcd = &c2;
    pcd->Report();

    cout << "Calling a function with a cd reference argument:
";
    Bravo(c1);
    Bravo(c2);

    cout << "Testing assignment:
";
    Classic copy;
    copy = c2;
    copy.Report();

    //pause
    cin.get();
    return 0;

}

void Bravo(const CD & disk)
{
    disk.Report();
}

3.不想使用原题所以没用，目的是练习抽象基类的继承。

所谓抽象基类，就是把定义的基类之中的虚成员函数声明为纯虚的（virtual修饰的函数后面加个 = 0），那么这个基类就只能用于继承，而不能实例化。一旦在代码里试图去实例化，编译之前就会提示“不允许使用抽象类型XXX的对象”。

抽象基类是抽象出一系列对象的共性的做法，方便派生出许多相似的对象。 需要注意，基类定义的纯虚函数不给出定义，而由所有派生类给出自己的定义。

下面是自己简单的练习。定义一个MovingObject的抽象基类，nowwhere()显示当前目标的位置，set_speed()设定目标的速度。从MovingObject派生出Car和Plane对象，各自的构造函数、析构函数、nowwhere()和set_speed()方法都不同。Car类会在坐标轴上按上下左右四个方向移动，Plane类指定一个目标地点，用动态数组的方式存储和打印该地点。

class.h

#ifndef _CLASS_H_
#define _CLASS_H_

#include <iostream>
#include <string>

using std::cout;
using std::cin;
using std::string;

/* Abstract Base Class */
class MovingObject
{
protected:
    double x;
    double y;
    double v;
    string name;

public:
    MovingObject();
    virtual ~MovingObject();
    virtual void nowwhere() = 0;    //pure virtual function
    virtual void set_speed(unsigned int vv) = 0;    //pure virtual function
};

MovingObject::MovingObject()
{
}

MovingObject::~MovingObject()
{
}

/* Derived Class A */
class Car :public MovingObject
{
public:
    enum car_direction
    {
        UP = 0,
        DOWN,
        LEFT,
        RIGHT,
        RESET
    }drive_to;

private:

public:
    Car();
    Car(const double xx, const double yy);
    ~Car();
    void move(car_direction drive_to,double t);
    void nowwhere();
    void set_speed(unsigned int vv);
};

Car::Car()
{
    name = "car";
    x = 0;
    y = 0;
    v = 30;
    cout << "A new car constructed.
";
}

Car::Car(const double xx, const double yy)
{
    name = "car";
    x = xx;
    y = yy;
    v = 30;
    cout << "A new car constructed.
";
}

Car::~Car()
{
    cout << "Car decontructed
";
}

void Car::move(car_direction drive_to = RESET,double t = 0)
{
    switch (drive_to)
    {
        case(UP):
        {
            cout << "The car's moving up, " << "with " << v << " m/s in " << t << " s.
";
            y = y + v * t;
            break;
        }
        case(DOWN):
        {
            cout << "The car's moving down, " << "with " << v << " m/s in " << t << " s.
";
            y = y - v * t;
            break;
        }
        case(LEFT):
        {
            cout << "The car's moving left, " << "with " << v << " m/s in " << t << " s.
";
            x = x - v * t;
            break;
        }
        case(RIGHT):
        {
            cout << "The car's moving right, " << "with " << v << " m/s in " << t << " s.
";
            x = x + v * t;
            break;
        }
        case(RESET):
        {
            cout << "The car's at (0,0).
";
            x = 0;
            y = 0;
            v = 1;
            break;
        }
        default:
        {
            break;
        }
    }
}

void Car::nowwhere()
{
    cout << name << " is at (" << x << "," << y << ").
";
}

void Car::set_speed(unsigned int vv)
{
    v = vv;
}

/* Derived Class B */
class Plane:public MovingObject
{
private:
    char *flywhere;

public:
    Plane();
    ~Plane();
    void nowwhere();
    void set_speed(unsigned int vv);

};

Plane::Plane()
{
    flywhere = new char[20];
    char wishplace[20] = {};
    v = 180;
    cout << "A plane just arrived.
";
    cout << "Assign one destination you wish: ";
    cin >> wishplace;
    for (int i = 0; i < (strlen(wishplace)+1); i++)
    {
        flywhere[i] = wishplace[i];
    }
}

Plane::~Plane()
{
    cout << "Plane deconstructed.
";
    delete[] flywhere;
}

void Plane::nowwhere()
{
    cout << "The plane's flying at " << v << " m/s.
";
    cout << "Finally it arrived at ";
    for (int i = 0; flywhere[i] != ''; i++)
    {
        cout << flywhere[i];
    }
    cout << ".
";
}

void Plane::set_speed(unsigned int vv)
{
    cout << "Changing speed to (150~250): ";
    if ((vv >= 150) && (vv <= 250))
    {
        v = vv;
    }
    else
    {
        cout << "Invalid speed! (Current: " << v << " m/s.)";
    }
}


#endif

main.cpp

#include "Class.h"

int main()
{
    Car car1;
    car1.move(Car::UP,10);
    car1.nowwhere();

    Plane plane1;
    plane1.set_speed(180);
    plane1.nowwhere();

    //pause
    cin.get();
    cin.get();

    return 0;

}

输出结果：

4.派生练习。定义存储酒相关信息的类和派生类。

对原题问题的回答：

（a）见代码。

（b）Port有所有默认参数的构造函数和默认构造函数冲突了。

（c）运算符=重载的函数应用的对象算不同的类型，运算符<<重载的函数是友元函数，友元函数不归属于类，也不能被继承，所以不需要声明为虚。

（d）见代码。

Class.h

#ifndef _CLASS_H_
#define _CLASS_H_

#include <iostream>
using std::ostream;
using std::cout;
using std::cin;

//Base Class
class Port
{
private:
    char * brand;
    char style[20];        //tawny,ruby,vintage...
    int bottles;

public:
    Port(const char *br, const char *st, int b);    //重新定义，去掉默认参数，防止与默认构造函数重复
    Port();    //创建的默认构造函数
    Port(const Port & p);
    virtual ~Port() { delete[]brand; }
    Port & operator = (const Port & p);
    Port & operator += (int b);        //add bottles
    Port & operator -= (int b);
    int BottleCount()const { return bottles; }
    virtual void show()const;
    friend ostream & operator << (ostream & os, const Port & p);
};

Port::Port(const char *br, const char *st, int b = 0)
{
    brand = new char[strlen(br) + 1];
    for (int i = 0; i < (strlen(br) + 1); i++)
    {
        brand[i] = br[i];
    }
    for (int i = 0; i < (strlen(st) + 1); i++)
    {
        style[i] = st[i];
    }
    bottles = b;

}

Port::Port()
{
    brand = new char[20];
    brand[0] = '';
    style[0] = '';
    bottles = 0;
        
}

Port::Port(const Port & p)
{
    for (int i = 0; i<strlen(p.brand)+1; i++)
    {
        brand[i] = p.brand[i];
    }
    for (int i = 0; p.style[i]!=''; i++)
    {
        style[i] = p.style[i];
    }
    bottles = p.bottles;

}

Port & Port::operator = (const Port & p)
{
    for (int i = 0; i<strlen(p.brand)+1; i++)
    {
        brand[i] = p.brand[i];
    }
    for (int i = 0; i < strlen(p.style) + 1; i++)
    {
        style[i] = p.style[i];
    }
    bottles = p.bottles;

    return *this;
}

Port & Port::operator += (int b)
{
    bottles += b;
    return *this;
}

Port & Port::operator -= (int b)
{
    bottles -= b;
    return *this;
}

void Port::show()const
{
    cout << "Brand:";
    for (int i = 0; brand[i] != ''; i++)
    {
        cout << brand[i];
    }
    cout << "
";
    cout << "Kind:";
    for (int i = 0; style[i] != ''; i++)
    {
        cout << style[i];
    }
    cout << "
";
    cout << "Bottles:" << bottles << "
";
}

ostream & operator << (ostream & os, const Port & p)
{
    os << "Brand:";
    for (int i = 0; p.brand[i] != ''; i++)
    {
        cout << p.brand[i];
    }
    os << "
";
    os << "Kind:";
    for (int i = 0; p.style[i] != ''; i++)
    {
        os << p.style[i];
    }
    os << "
";
    os << "Bottles:" << p.bottles << "
";

    return os;

}

//Derived Class
class VintagePort :public Port
{
private:
    char *nickname;
    int year;

public:
    VintagePort();
    VintagePort(const char * br, int b, const char *nn, int y);
    VintagePort(VintagePort & vp);
    ~VintagePort() { delete[]nickname; }
    VintagePort & operator = (const VintagePort & vp);
    void show() const;
    friend ostream & operator << (ostream & os, const VintagePort & vp);
};

VintagePort::VintagePort()
{
    nickname = new char[20];
    nickname[0] = '';
    year = 0;
}

VintagePort::VintagePort(const char * br, int b, const char *nn, int y):Port(br,"none",b)
{
    nickname = new char[strlen(nn) + 1];
    for (int i = 0; i < strlen(nn) + 1; i++)
    {
        nickname[i] = nn[i];
    }
    year = y;
}

VintagePort::VintagePort(VintagePort & vp)
{
    for (int i = 0; i < strlen(vp.nickname) + 1; i++)
    {
        nickname[i] = vp.nickname[i];
    }
    year = vp.year;
}

void VintagePort::show()const
{
    Port::show();
    cout << "Nickname:";
    for (int i = 0; nickname[i] != ''; i++)
    {
        cout << nickname[i];
    }
    cout << "
";
    cout << "Year:" << year;
    cout << "
";
}

VintagePort & VintagePort::operator = (const VintagePort & vp)
{
    Port::operator=(vp);

    for (int i = 0; i < strlen(vp.nickname) + 1; i++)
    {
        nickname[i] = vp.nickname[i];
    }
    year = vp.year;

    return *this;
}

ostream & operator << (ostream & os, const VintagePort & vp)
{
    cout << "Nickname:";
    for (int i = 0; vp.nickname[i] != ''; i++)
    {
        os << vp.nickname[i];
    }
    os << "
";
    os << "Year:" << vp.year;
    os << "
";

    return os;

}

#endif

main.cpp

#include "Class.h"

int main()
{
    cout << "-- p1 using default constructor -- 
";
    Port p1;
    p1.show();

    cout << "-- p2 using custom constructor -- 
";
    Port p2("Gallo", "vintage", 20);
    p2.show();

    cout << "-- p2 add 20 bottles -- 
";
    p2 += 20;
    p2.show();

    cout << "-- copy p2 -> p1 -- 
";
    p1 = p2;
    p1.show();

    cout << "-- cout << p1 -- 
";
    cout << p1;

    cout << "-- vp1 using default constructor -- 
";
    VintagePort vp1;
    vp1.show();

    cout << "-- vp2 using custom constructor -- 
";
    VintagePort vp2("Ruby", 10, "pussy", 1998);
    vp2.show();

    cout << "-- copy vp2 -> vp1 -- 
";
    p1 = p2;
    vp1 = vp2;
    vp1.show();

    cout << "-- copy p2 -> p1 -- 
";
    p1 = p2;
    cout << vp2;

    cout << "-- cout << vp1 -- 
";
    cout << vp1;

    //pause
    cin.get();

    return 0;

}