• 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。

    1. #include 
    2. #include "tv.h"
    3.  
    4. int main()
    5. {
    6.     using std::cout;
    7.  
    8.     Tv s42;
    9.     cout << "Initial settings for 42\" TV:\n";
    10.     s42.settings();
    11.     s42.onoff();
    12.     s42.chanup();
    13.     cout << "\nAdjusted settings for 42\" TV:\n";
    14.     s42.settings();
    15.  
    16.     Remote grey;
    17.     grey.set_chan(s42, 10);
    18.     grey.volup(s42);
    19.     grey.volup(s42);
    20.     s42.set_status(grey);
    21.     cout << "\n42\" settings after using remote:\n";
    22.     s42.settings();
    23.     grey.show_status();
    24.  
    25.     Tv s58(Tv::On);
    26.     s58.set_mode();
    27.     grey.set_chan(s58, 28);
    28.     s58.set_status(grey);
    29.     cout << "\n58\" settings:\n";
    30.     s58.settings();
    31.     grey.show_status();
    32.  
    33.     return 0;
    34. }
    1. #ifndef TV_H_
    2. #define TV_H_
    3. #include 
    4.  
    5. 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;
    6.  
    7. class Tv
    8. {
    9. public:
    10.     friend class Remote;
    11.     enum { Off, On };
    12.     enum { MinVal, MaxVal = 20 };
    13.     enum { Antenna, Cable };
    14.     enum { TV, DVD };
    15.     Tv(int s = Off, int mc = 125) : state(s), volume(5),
    16.                                     maxchannel(mc), channel(2), mode(Cable), input(TV) {}
    17.     void onoff() { state = (state == On) ? Off : On; }
    18.     bool ison() const { return state == On; }
    19.     bool volup();
    20.     bool voldown();
    21.     void chanup();
    22.     void chandown();
    23.     void set_mode() { mode = (mode == Antenna) ? Cable : Antenna; }
    24.     void set_input() { input = (input == TV) ? DVD : TV; }
    25.     void settings() const;
    26.     void set_status(Remote &r); //对Remote类中状态成员进行切换的方法;
    27.  
    28. private:
    29.     int state;
    30.     int volume;
    31.     int maxchannel;
    32.     int channel;
    33.     int mode;
    34.     int input;
    35. };
    36.  
    37. class Remote
    38. {
    39. private:
    40.     int mode;
    41.     int status; //状态变量成员;
    42.  
    43. public:
    44.     friend class Tv;
    45.     enum { Convention, Interaction }; //Convention表示常规模式, Interaction表示互动模式;
    46.     Remote(int m = Tv::TV, int s = Convention) : mode(m), status(s) {} //默认为常规模式;
    47.     bool volup(Tv &t) { return t.volup(); }
    48.     bool voldown(Tv &t) { return t.voldown(); }
    49.     void onoff(Tv &t) { t.onoff(); }
    50.     void chanup(Tv &t) { t.chanup(); }
    51.     void chandown(Tv &t) { t.chandown(); }
    52.     void set_chan(Tv &t, int c) { t.channel = c; }
    53.     void set_mode(Tv &t) { t.set_mode(); }
    54.     void set_input(Tv &t) { t.set_input(); }
    55.     void show_status() const;
    56. };
    57.  
    58. inline void Tv::set_status(Remote &r)
    59. {
    60.     if (ison())
    61.     {
    62.         r.status = Remote::Convention == r.status ? Remote::Interaction : Remote::Convention;
    63.     }
    64. }
    65.  
    66. inline void Remote::show_status() const
    67. {
    68.     std::cout << "Status = " << (status == Convention ? "Convention" : "Interaction") << std::endl;
    69. }
    70.  
    71. #endif
    1. #include 
    2. #include "tv.h"
    3.  
    4. bool Tv::volup()
    5. {
    6.     if (volume < MaxVal)
    7.     {
    8.         volume++;
    9.         return true;
    10.     }
    11.     return false;
    12. }
    13.  
    14. bool Tv::voldown()
    15. {
    16.     if (volume > MinVal)
    17.     {
    18.         volume--;
    19.         return true;
    20.     }
    21.     return false;
    22. }
    23.  
    24. void Tv::chanup()
    25. {
    26.     channel = channel < maxchannel ? 1 + channel : 1;
    27. }
    28.  
    29. void Tv::chandown()
    30. {
    31.     channel = channel > 1 ? channel - 1 : maxchannel;
    32. }
    33.  
    34. void Tv::settings() const
    35. {
    36.     using std::cout;
    37.     using std::endl;
    38.     cout << "TV is " << (state == Off ? "Off" : "On") << endl;
    39.     if (state == On)
    40.     {
    41.         cout << "Volume setting = " << volume << endl;
    42.         cout << "Channel setting = " << channel << endl;
    43.         cout << "Mode = ";
    44.         cout << (mode == Antenna ? "antenna" : "cable") << endl;
    45.         cout << "Input = ";
    46.         cout << (input == TV ? "TV" : "DVD") << endl;
    47.     }
    48. }

    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

    1. #include 
    2. #include 
    3. #include "exc_mean.h"
    4.  
    5. double hmean(double a, double b);
    6. double gmean(double a, double b);
    7.  
    8. int main()
    9. {
    10.     using std::cin;
    11.     using std::cout;
    12.     using std::endl;
    13.  
    14.     double x, y, z;
    15.  
    16.     cout << "Enter two numbers: ";
    17.     while (cin >> x >> y)
    18.     {
    19.         try
    20.         {
    21.             z = hmean(x, y);
    22.             cout << "Harmonic mean of " << x << " and " << y;
    23.             cout << " is " << z << endl;
    24.             z = gmean(x, y);
    25.             cout << "Geometric mean of " << x << " and " << y;
    26.             cout << " is " << z << endl;
    27.             cout << "Enter next set of numbers : ";
    28.         }
    29.         catch (bad_hmean &bg)
    30.         {
    31.             cout << bg.what(); //调用what方法打印hmean中的异常;
    32.             cout << "Try again.\n";
    33.             continue;
    34.         }
    35.         catch (bad_gmean &hg)
    36.         {
    37.             cout << hg.what(); //调用what方法打印gmean中的异常;
    38.             cout << "Sorry, you don't get to play any more.\n";
    39.             break;
    40.         }
    41.     }
    42.     cout << "Bye!\n";
    43.  
    44.     return 0;
    45. }
    46.  
    47. double hmean(double a, double b)
    48. {
    49.     if (a == -b)
    50.     {
    51.         throw bad_hmean();
    52.     }
    53.     return 2.0 * a * b / (a + b);
    54. }
    55.  
    56. double gmean(double a, double b)
    57. {
    58.     if (a < 0 || b < 0)
    59.     {
    60.         throw bad_gmean();
    61.     }
    62.     return std::sqrt(a * b);
    63. }
    1. #ifndef EXC_MEAN_H_
    2. #define EXC_MEAN_H_
    3. #include 
    4. #include 
    5. #include 
    6. using namespace std;
    7.  
    8. class bad_hmean : public logic_error
    9. {
    10. public:
    11.     explicit bad_hmean(const string &s = "Error in bad_hmean object\nhmean() arguments should be a != -b\n") : logic_error(s) {}
    12. };
    13.  
    14. class bad_gmean : public logic_error
    15. {
    16. public:
    17.     explicit bad_gmean(const string &s = "Error in bad_hmean object\ngmean() arguments should be >= 0\n") : logic_error(s) {}
    18. };
    19.  
    20. #endif
    21.  
    22.

    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。

    1. #include 
    2. #include 
    3. #include "exc_mean.h"
    4.  
    5. double hmean(double a, double b);
    6. double gmean(double a, double b);
    7.  
    8. int main()
    9. {
    10.     using std::cin;
    11.     using std::cout;
    12.     using std::endl;
    13.  
    14.     double x, y, z;
    15.  
    16.     cout << "Enter two numbers: ";
    17.     while (cin >> x >> y)
    18.     {
    19.         try
    20.         {
    21.             z = hmean(x, y);
    22.             cout << "Harmonic mean of " << x << " and " << y;
    23.             cout << " is " << z << endl;
    24.             z = gmean(x, y);
    25.             cout << "Geometric mean of " << x << " and " << y;
    26.             cout << " is " << z << endl;
    27.             cout << "Enter next set of numbers : ";
    28.         }
    29.         catch (mean &m) //捕获基类以及派生类的任何异常;
    30.         {
    31.             cout << "Sorry, you don't get to play any more.\n";
    32.             break;
    33.         }
    34.     }
    35.     cout << "Bye!\n";
    36.  
    37.     return 0;
    38. }
    39.  
    40. double hmean(double a, double b)
    41. {
    42.     if (a == -b)
    43.     {
    44.         bad_hmean temp("hmean", a, b);
    45.         temp.mesg();
    46.         throw temp;
    47.     }
    48.     return 2.0 * a * b / (a + b);
    49. }
    50.  
    51. double gmean(double a, double b)
    52. {
    53.     if (a < 0 || b < 0)
    54.     {
    55.         bad_gmean temp("gmean", a, b);
    56.         temp.mesg();
    57.         throw temp;
    58.     }
    59.     return std::sqrt(a * b);
    60. }
    1. #ifndef EXC_MEAN_H_
    2. #define EXC_MEAN_H_
    3. #include 
    4. #include 
    5. #include 
    6. using namespace std;
    7.  
    8. class mean : public logic_error
    9. {
    10. private:
    11.     double v1;
    12.     double v2;
    13.  
    14. public:
    15.     mean(const string &s = "none", double a = 0.0, double b = 0.0) : logic_error(s), v1(a), v2(b) {}
    16.     const double &val1() const { return v1; }
    17.     const double &val2() const { return v2; }
    18. };
    19.  
    20. class bad_hmean : public mean
    21. {
    22. public:
    23.     bad_hmean(const string &s = "none", double a = 0.0, double b = 0.0) : mean(s, a, b) {}
    24.     void mesg() const;
    25. };
    26.  
    27. inline void bad_hmean::mesg() const
    28. {
    29.     cout << "hmean(" << val1() << ", " << val2() << "):" << endl;
    30.     cout << "hmean() arguments should be a != b" << endl;
    31. }
    32.  
    33. class bad_gmean : public mean
    34. {
    35. public:
    36.     bad_gmean(const string &s = "none", double a = 0.0, double b = 0.0) : mean(s, a, b) {}
    37.     void mesg() const;
    38. };
    39.  
    40. inline void bad_gmean::mesg() const
    41. {
    42.     cout << "gmean(" << val1() << ", " << val2() << "):" << endl;
    43.     cout << "gmean() arguments should be >= 0" << endl;
    44. }
    45.  
    46. #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()

    1. #include 
    2. #include "sales.h"
    3.  
    4. int main()
    5. {
    6.     using std::cin;
    7.     using std::cout;
    8.     using std::endl;
    9.  
    10.     double vals1[12] =
    11.     {
    12.         1220, 1100, 1122, 2212, 1232, 2334,
    13.         2884, 2393, 3302, 2922, 3002, 3544
    14.     };
    15.     double vals2[12] =
    16.     {
    17.         12, 11, 22, 21, 32, 34,
    18.         28, 29, 33, 29, 32, 35
    19.     };
    20.     Sales sales1(2011, vals1, 12);
    21.     LabeledSales sales2("Blogstar", 2012, vals2, 12);
    22.  
    23.     cout << "First try block:\n";
    24.     try
    25.     {
    26.         int i;
    27.         cout << "Year = " << sales1.Year() << endl;
    28.         for (i = 0; i < 12; ++i)
    29.         {
    30.             cout << sales1[i] << ' ';
    31.             if (i % 6 == 5)
    32.             {
    33.                 cout << endl;
    34.             }
    35.         }
    36.         cout << "Year = " << sales2.Year() << endl;
    37.         cout << "Label = " << sales2.Label() << endl;
    38.         for (i = 0; i <= 12; ++i)
    39.         {
    40.             cout << sales2[i] << ' ';
    41.             if (i % 6 == 5)
    42.             {
    43.                 cout << endl;
    44.             }
    45.         }
    46.         cout << "End of try block 1.\n";
    47.     }
    48.     catch (Sales::bad_index &bad)
    49.     {
    50.         cout << bad.what();
    51.         LabeledSales::nbad_index *ni;
    52.         if (ni = dynamic_cast(&bad)) //RTTI识别类型;
    53.         {
    54.             cout << "Company: " << ni->label_val() << endl;
    55.             cout << "bad index: " << ni->bi_val() << endl;
    56.         }
    57.         else
    58.         {
    59.             cout << "bad index: " << bad.bi_val() << endl;
    60.         }
    61.     }
    62.     cout << "\nNext try block:\n";
    63.     try
    64.     {
    65.         sales2[2] = 37.5;
    66.         sales1[20] = 23345;
    67.         cout << "End of try block 2.\n";
    68.     }
    69.     catch (Sales::bad_index &bad)
    70.     {
    71.         cout << bad.what();
    72.         LabeledSales::nbad_index *ni;
    73.         if (ni = dynamic_cast(&bad)) //RTTI识别类型;
    74.         {
    75.             cout << "Company: " << ni->label_val() << endl;
    76.             cout << "bad index: " << ni->bi_val() << endl;
    77.         }
    78.         else
    79.         {
    80.             cout << "bad index: " << bad.bi_val() << endl;
    81.         }
    82.     }
    83.     cout << "done\n";
    84.  
    85.     return 0;
    86. }

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  • 原文地址：https://blog.csdn.net/sakura0908/article/details/132722863