C++ primer plus第十五章编程练习答案

1.对Tv 和 Remote 类做如下修改:
a，让它们互为友元;
b.在 Remote类中添加一个状态变量成员，该成员描述遥控器是处于常规模式还是互动模式:
c，在 Remote 中添加一个显示模式的方法
d.在T类中添加一个对 Remote 中新成员进行切换的方法，该方法应仅当 TV 处于打开状态时才能运行。
编写一个小程序来测试这些新特性。

#include 
#include "tv.h"

int main()
{
    using std::cout;

    Tv s42;
    cout << "Initial settings for 42\" TV:\n";
    s42.settings();
    s42.onoff();
    s42.chanup();
    cout << "\nAdjusted settings for 42\" TV:\n";
    s42.settings();

    Remote grey;
    grey.set_chan(s42, 10);
    grey.volup(s42);
    grey.volup(s42);
    s42.set_status(grey);
    cout << "\n42\" settings after using remote:\n";
    s42.settings();
    grey.show_status();

    Tv s58(Tv::On);
    s58.set_mode();
    grey.set_chan(s58, 28);
    s58.set_status(grey);
    cout << "\n58\" settings:\n";
    s58.settings();
    grey.show_status();

    return 0;
}

#ifndef TV_H_
#define TV_H_
#include 

class Remote; //先声明Remote类然后再定义, 以便编译器有足够的信息编译使用Remote类的方法;

class Tv
{
public:
    friend class Remote;
    enum { Off, On };
    enum { MinVal, MaxVal = 20 };
    enum { Antenna, Cable };
    enum { TV, DVD };
    Tv(int s = Off, int mc = 125) : state(s), volume(5),
                                    maxchannel(mc), channel(2), mode(Cable), input(TV) {}
    void onoff() { state = (state == On) ? Off : On; }
    bool ison() const { return state == On; }
    bool volup();
    bool voldown();
    void chanup();
    void chandown();
    void set_mode() { mode = (mode == Antenna) ? Cable : Antenna; }
    void set_input() { input = (input == TV) ? DVD : TV; }
    void settings() const;
    void set_status(Remote &r); //对Remote类中状态成员进行切换的方法;

private:
    int state;
    int volume;
    int maxchannel;
    int channel;
    int mode;
    int input;
};

class Remote
{
private:
    int mode;
    int status; //状态变量成员;

public:
    friend class Tv;
    enum { Convention, Interaction }; //Convention表示常规模式, Interaction表示互动模式;
    Remote(int m = Tv::TV, int s = Convention) : mode(m), status(s) {} //默认为常规模式;
    bool volup(Tv &t) { return t.volup(); }
    bool voldown(Tv &t) { return t.voldown(); }
    void onoff(Tv &t) { t.onoff(); }
    void chanup(Tv &t) { t.chanup(); }
    void chandown(Tv &t) { t.chandown(); }
    void set_chan(Tv &t, int c) { t.channel = c; }
    void set_mode(Tv &t) { t.set_mode(); }
    void set_input(Tv &t) { t.set_input(); }
    void show_status() const;
};

inline void Tv::set_status(Remote &r)
{
    if (ison())
    {
        r.status = Remote::Convention == r.status ? Remote::Interaction : Remote::Convention;
    }
}

inline void Remote::show_status() const
{
    std::cout << "Status = " << (status == Convention ? "Convention" : "Interaction") << std::endl;
}

#endif

#include 
#include "tv.h"

bool Tv::volup()
{
    if (volume < MaxVal)
    {
        volume++;
        return true;
    }
    return false;
}

bool Tv::voldown()
{
    if (volume > MinVal)
    {
        volume--;
        return true;
    }
    return false;
}

void Tv::chanup()
{
    channel = channel < maxchannel ? 1 + channel : 1;
}

void Tv::chandown()
{
    channel = channel > 1 ? channel - 1 : maxchannel;
}

void Tv::settings() const
{
    using std::cout;
    using std::endl;
    cout << "TV is " << (state == Off ? "Off" : "On") << endl;
    if (state == On)
    {
        cout << "Volume setting = " << volume << endl;
        cout << "Channel setting = " << channel << endl;
        cout << "Mode = ";
        cout << (mode == Antenna ? "antenna" : "cable") << endl;
        cout << "Input = ";
        cout << (input == TV ? "TV" : "DVD") << endl;
    }
}

2.修改程序清单 15.11，使两种异常类型都是从头文件stdexcepi>提供的 logic_error 类派生出来的类让每个 what()方法都报告函数名和问题的性质。异常对象不用存储错误的参数值，而只需支持 what()方法

#include 
#include 
#include "exc_mean.h"

double hmean(double a, double b);
double gmean(double a, double b);

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;

    double x, y, z;

    cout << "Enter two numbers: ";
    while (cin >> x >> y)
    {
        try
        {
            z = hmean(x, y);
            cout << "Harmonic mean of " << x << " and " << y;
            cout << " is " << z << endl;
            z = gmean(x, y);
            cout << "Geometric mean of " << x << " and " << y;
            cout << " is " << z << endl;
            cout << "Enter next set of numbers : ";
        }
        catch (bad_hmean &bg)
        {
            cout << bg.what(); //调用what方法打印hmean中的异常;
            cout << "Try again.\n";
            continue;
        }
        catch (bad_gmean &hg)
        {
            cout << hg.what(); //调用what方法打印gmean中的异常;
            cout << "Sorry, you don't get to play any more.\n";
            break;
        }
    }
    cout << "Bye!\n";

    return 0;
}

double hmean(double a, double b)
{
    if (a == -b)
    {
        throw bad_hmean();
    }
    return 2.0 * a * b / (a + b);
}

double gmean(double a, double b)
{
    if (a < 0 || b < 0)
    {
        throw bad_gmean();
    }
    return std::sqrt(a * b);
}

#ifndef EXC_MEAN_H_
#define EXC_MEAN_H_
#include 
#include 
#include 
using namespace std;

class bad_hmean : public logic_error
{
public:
    explicit bad_hmean(const string &s = "Error in bad_hmean object\nhmean() arguments should be a != -b\n") : logic_error(s) {}
};

class bad_gmean : public logic_error
{
public:
    explicit bad_gmean(const string &s = "Error in bad_hmean object\ngmean() arguments should be >= 0\n") : logic_error(s) {}
};

#endif

3.这个练习与编程练习2相同，但异常类是从一个这样的基类派生而来的:它是从 logic_crror 派生而来的，并存储两个参数值。异常类应该有一个这样的方法:报告这些值以及函数名。程序使用一个 catch块来捕获基类异常，其中任何一种从该基类异常派生而来的异常都将导致循环结束。

#include 
#include 
#include "exc_mean.h"

double hmean(double a, double b);
double gmean(double a, double b);

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;

    double x, y, z;

    cout << "Enter two numbers: ";
    while (cin >> x >> y)
    {
        try
        {
            z = hmean(x, y);
            cout << "Harmonic mean of " << x << " and " << y;
            cout << " is " << z << endl;
            z = gmean(x, y);
            cout << "Geometric mean of " << x << " and " << y;
            cout << " is " << z << endl;
            cout << "Enter next set of numbers : ";
        }
        catch (mean &m) //捕获基类以及派生类的任何异常;
        {
            cout << "Sorry, you don't get to play any more.\n";
            break;
        }
    }
    cout << "Bye!\n";

    return 0;
}

double hmean(double a, double b)
{
    if (a == -b)
    {
        bad_hmean temp("hmean", a, b);
        temp.mesg();
        throw temp;
    }
    return 2.0 * a * b / (a + b);
}

double gmean(double a, double b)
{
    if (a < 0 || b < 0)
    {
        bad_gmean temp("gmean", a, b);
        temp.mesg();
        throw temp;
    }
    return std::sqrt(a * b);
}

#ifndef EXC_MEAN_H_
#define EXC_MEAN_H_
#include 
#include 
#include 
using namespace std;

class mean : public logic_error
{
private:
    double v1;
    double v2;

public:
    mean(const string &s = "none", double a = 0.0, double b = 0.0) : logic_error(s), v1(a), v2(b) {}
    const double &val1() const { return v1; }
    const double &val2() const { return v2; }
};

class bad_hmean : public mean
{
public:
    bad_hmean(const string &s = "none", double a = 0.0, double b = 0.0) : mean(s, a, b) {}
    void mesg() const;
};

inline void bad_hmean::mesg() const
{
    cout << "hmean(" << val1() << ", " << val2() << "):" << endl;
    cout << "hmean() arguments should be a != b" << endl;
}

class bad_gmean : public mean
{
public:
    bad_gmean(const string &s = "none", double a = 0.0, double b = 0.0) : mean(s, a, b) {}
    void mesg() const;
};

inline void bad_gmean::mesg() const
{
    cout << "gmean(" << val1() << ", " << val2() << "):" << endl;
    cout << "gmean() arguments should be >= 0" << endl;
}

#endif

4.程序清单 15.16 在每个 ty 后面都使用两个 catch 块，以确保 nbad index 异常导致方法 abel_val()被调用。请修改该程序在每个 ty 块后面只使用一个 catch 块并使用 RTTI 来确保合适时调用 abel_val()

#include 
#include "sales.h"

int main()
{
    using std::cin;
    using std::cout;
    using std::endl;

    double vals1[12] =
    {
        1220, 1100, 1122, 2212, 1232, 2334,
        2884, 2393, 3302, 2922, 3002, 3544
    };
    double vals2[12] =
    {
        12, 11, 22, 21, 32, 34,
        28, 29, 33, 29, 32, 35
    };
    Sales sales1(2011, vals1, 12);
    LabeledSales sales2("Blogstar", 2012, vals2, 12);

    cout << "First try block:\n";
    try
    {
        int i;
        cout << "Year = " << sales1.Year() << endl;
        for (i = 0; i < 12; ++i)
        {
            cout << sales1[i] << ' ';
            if (i % 6 == 5)
            {
                cout << endl;
            }
        }
        cout << "Year = " << sales2.Year() << endl;
        cout << "Label = " << sales2.Label() << endl;
        for (i = 0; i <= 12; ++i)
        {
            cout << sales2[i] << ' ';
            if (i % 6 == 5)
            {
                cout << endl;
            }
        }
        cout << "End of try block 1.\n";
    }
    catch (Sales::bad_index &bad)
    {
        cout << bad.what();
        LabeledSales::nbad_index *ni;
        if (ni = dynamic_cast(&bad)) //RTTI识别类型;
        {
            cout << "Company: " << ni->label_val() << endl;
            cout << "bad index: " << ni->bi_val() << endl;
        }
        else
        {
            cout << "bad index: " << bad.bi_val() << endl;
        }
    }
    cout << "\nNext try block:\n";
    try
    {
        sales2[2] = 37.5;
        sales1[20] = 23345;
        cout << "End of try block 2.\n";
    }
    catch (Sales::bad_index &bad)
    {
        cout << bad.what();
        LabeledSales::nbad_index *ni;
        if (ni = dynamic_cast(&bad)) //RTTI识别类型;
        {
            cout << "Company: " << ni->label_val() << endl;
            cout << "bad index: " << ni->bi_val() << endl;
        }
        else
        {
            cout << "bad index: " << bad.bi_val() << endl;
        }
    }
    cout << "done\n";

    return 0;
}