《C++ Primer Plus》（第6版）第11章编程练习

《C++ Primer Plus》（第6版）第11章编程练习

1. 随机漫步者位置写入文件

修改程序清单11.15，使之将一系列连续的随机漫步者位置写入到文件中。对于每个位置，用步号进行标志。另外，让该程序将初始条件（目标距离和步长）以及结果小结写入到该文件中。该文件的内容与下面类似：

Target Distance: 100, Step Size: 20
0: (x,y) = (0, 0)
1: (x,y) = (-11.4715, 16.383)
2: (x,y) = (-868807, -3.42232)
....
26: (x,y) = (42.2919, -78.2594)
27: (x,y) = (58.6749, -89.7309)
After 27 steps, the subject has the following location:
(x,y) = (58.6749, -89.7309)
or
(m,a) = (107.212, -56.8194)
Average outward distance per step = 3.97081

代码：

vector.h：

#ifndef VECTOR_H_
#define VECTOR_H_
#include <iostream>

namespace VECTOR
{
    class Vector
    {
    public:
        enum Mode
        {
            RECT,
            POL
        };

    private:
        double x;
        double y;
        double mag;
        double ang;
        Mode mode;

        void set_mag();
        void set_ang();
        void set_x();
        void set_y();

    public:
        Vector();
        Vector(double n1, double n2, Mode from = RECT);
        void reset(double n1, double n2, Mode from = RECT);
        ~Vector();
        double xval() const { return x; };
        double yval() const { return y; };
        double magval() const { return mag; };
        double angval() const { return ang; };
        void polar_mode();
        void rect_mode();

        Vector operator+(const Vector &b) const;
        Vector operator-(const Vector &b) const;
        Vector operator-() const;
        Vector operator*(double n) const;

        friend Vector operator*(double n, const Vector &a);
        friend std::ostream &operator<<(std::ostream &os, const Vector &v);
    };

}
#endif // !VECTOR_H_

vector.cpp：

#include "vector.h"
#include <iostream>
#include <cmath>
using namespace std;

namespace VECTOR
{
    const double Rad_to_deg = 45.0 / atan(1.0);
    void Vector::set_mag()
    {
        mag = sqrt(x * x + y * y);
    }
    void Vector::set_ang()
    {
        if (x == 0 && y == 0)
            ang = 0.0;
        else
            ang = atan2(y, x);
    }
    void Vector::set_x()
    {
        x = mag * cos(ang);
    }
    void Vector::set_y()
    {
        y = mag * sin(ang);
    }
    Vector::Vector()
    {
        x = y = mag = ang = 0.0;
        mode = RECT;
    }
    Vector::Vector(double n1, double n2, Mode from)
    {
        mode = from;
        if (from == RECT)
        {
            x = n1;
            y = n2;
            set_ang();
            set_mag();
        }
        else if (from == POL)
        {
            mag = n1;
            ang = n2 / Rad_to_deg;
            set_x();
            set_y();
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector()--";
            cout << "vector set to 0\n";
            x = y = mag = ang = 0.0;
            mode = RECT;
        }
    }
    void Vector::reset(double n1, double n2, Mode from)
    {
        mode = from;
        if (from == RECT)
        {
            x = n1;
            y = n2;
            set_mag();
            set_ang();
        }
        else if (from == POL)
        {
            mag = n1;
            ang = n2 / Rad_to_deg;
            set_x();
            set_y();
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector()--";
            cout << "vector set to 0" << endl;
            x = y = mag = ang = 0.0;
            mode = RECT;
        }
    }
    Vector::~Vector()
    {
    }

    void Vector::polar_mode()
    {
        mode = POL;
    }
    void Vector::rect_mode()
    {
        mode = RECT;
    }
    Vector Vector::operator+(const Vector &b) const
    {
        return Vector(x + b.x, y + b.y);
    }
    Vector Vector::operator-(const Vector &b) const
    {
        return Vector(x - b.x, y - b.y);
    }
    Vector Vector::operator-() const
    {
        return Vector(-x, -y);
    }
    Vector Vector::operator*(double n) const
    {
        return Vector(n * x, n * y);
    }
    Vector operator*(double n, const Vector &a)
    {
        return a * n;
    }
    ostream &operator<<(ostream &os, const Vector &v)
    {
        if (v.mode == Vector::RECT)
            os << "(x,y) = (" << v.x << ", " << v.y << ")";
        else if (v.mode == Vector::POL)
            os << "(m,a) = (" << v.mag << ", " << v.ang << ")";
        else
            os << "Vector object mode is invalid";
        return os;
    }

}

randwalk.cpp：

#include "vector.h"
#include <iostream>
#include <cstdlib> //rand(), srand() prototypes
#include <ctime>   //time() prototype
#include <fstream>

int main()
{
    using namespace std;
    using VECTOR::Vector;
    ofstream outFile;
    outFile.open("randwalker.txt");
    srand(time(0));
    double direction;
    Vector step;
    Vector result(0.0, 0.0);
    unsigned long steps = 0;
    double target;
    double dstep;
    cout << "Enter target distance (q to quit): ";
    while (cin >> target)
    {
        cout << "Enter step length: ";
        if (!(cin >> dstep))
            break;
        outFile << "Target Distance: " << target << ", Step Size: " << dstep << endl;
        while (result.magval() < target)
        {
            outFile << steps << ": " << result << endl;
            direction = rand() % 360;
            step.reset(dstep, direction, Vector::POL);
            result = result + step;
            steps++;
        }
        outFile << "After " << steps << " steps, the subject has the following location:\n";
        outFile << result << endl;
        result.polar_mode();
        outFile << " or\n"
             << result << endl;
        outFile << "Average outward distance per step = " << result.magval() / steps << endl;
        steps = 0;
        result.reset(0.0, 0.0);
        cout << "Enter target distance (q to quit): ";
    }
    cout << "Bye!\n";
    cin.clear();
    while (cin.get() != '\n')
        continue;
    outFile.close();

    system("pause");
    return 0;
}

运行结果：

randwalker.txt：

Target Distance: 100, Step Size: 20
0: (x,y) = (0, 0)
1: (x,y) = (-9.38943, 17.659)
2: (x,y) = (9.40442, 10.8185)
3: (x,y) = (9.05537, -9.1784)
4: (x,y) = (6.61799, 10.6725)
5: (x,y) = (-11.9257, 3.18039)
6: (x,y) = (7.9982, 4.9235)
7: (x,y) = (3.15977, -14.4824)
8: (x,y) = (-16.0655, -19.9952)
9: (x,y) = (-26.9582, -3.22175)
10: (x,y) = (-19.7909, 15.4499)
11: (x,y) = (-28.2433, -2.6763)
12: (x,y) = (-37.6327, -20.3352)
13: (x,y) = (-52.2598, -33.9752)
14: (x,y) = (-40.5041, -50.1556)
15: (x,y) = (-29.9057, -67.1165)
16: (x,y) = (-44.5327, -80.7565)
17: (x,y) = (-25.2142, -75.5801)
18: (x,y) = (-5.29033, -73.837)
19: (x,y) = (13.3813, -66.6696)
20: (x,y) = (-4.11112, -56.9734)
21: (x,y) = (0.047114, -37.4105)
22: (x,y) = (-11.1367, -53.9912)
23: (x,y) = (5.0436, -65.7469)
24: (x,y) = (-14.7618, -62.9635)
25: (x,y) = (-10.9456, -43.3309)
26: (x,y) = (4.3753, -30.4752)
27: (x,y) = (-6.51748, -13.7018)
28: (x,y) = (-3.04451, -33.3979)
29: (x,y) = (16.8459, -31.3074)
30: (x,y) = (28.3175, -14.9243)
31: (x,y) = (46.2933, -6.15689)
32: (x,y) = (50.1095, 13.4756)
33: (x,y) = (47.3261, 33.281)
34: (x,y) = (38.5586, 51.2569)
35: (x,y) = (44.4061, 32.1308)
36: (x,y) = (44.7551, 52.1278)
37: (x,y) = (32.1687, 67.6707)
38: (x,y) = (39.9833, 49.2606)
39: (x,y) = (29.3849, 66.2215)
40: (x,y) = (47.9286, 73.7137)
41: (x,y) = (32.6077, 60.8579)
42: (x,y) = (21.1362, 77.241)
43: (x,y) = (11.1362, 59.9204)
44: (x,y) = (-7.88493, 66.1008)
45: (x,y) = (-22.9791, 52.9796)
46: (x,y) = (-15.487, 34.4359)
47: (x,y) = (-5.7908, 51.9283)
48: (x,y) = (6.52243, 36.1681)
49: (x,y) = (26.3734, 38.6055)
50: (x,y) = (20.193, 19.5844)
51: (x,y) = (40.1443, 18.1892)
52: (x,y) = (29.5459, 35.1502)
53: (x,y) = (9.54591, 35.1502)
54: (x,y) = (16.7133, 53.8218)
55: (x,y) = (16.0153, 33.834)
56: (x,y) = (29.6552, 48.4611)
57: (x,y) = (32.0926, 28.6101)
58: (x,y) = (46.7197, 42.2501)
59: (x,y) = (26.9659, 45.3788)
60: (x,y) = (32.8134, 26.2527)
61: (x,y) = (31.7667, 46.2253)
62: (x,y) = (12.3607, 51.0637)
63: (x,y) = (13.7559, 71.015)
64: (x,y) = (10.9724, 90.8204)
65: (x,y) = (16.4852, 71.5951)
66: (x,y) = (-2.64094, 77.4426)
67: (x,y) = (11.5012, 91.5847)
68: (x,y) = (14.9742, 71.8886)
69: (x,y) = (-4.51324, 67.3895)
70: (x,y) = (-24.0006, 62.8905)
71: (x,y) = (-5.59055, 55.0759)
72: (x,y) = (-11.7709, 74.097)
73: (x,y) = (-30.5647, 67.2566)
74: (x,y) = (-45.4276, 53.874)
75: (x,y) = (-42.2989, 34.1202)
76: (x,y) = (-60.5699, 42.255)
77: (x,y) = (-78.0622, 51.9512)
78: (x,y) = (-61.6792, 63.4227)
79: (x,y) = (-53.2268, 81.5488)
80: (x,y) = (-36.2659, 70.9505)
81: (x,y) = (-16.86, 66.112)
82: (x,y) = (-23.3713, 85.0224)
83: (x,y) = (-42.6898, 79.846)
84: (x,y) = (-27.369, 92.7018)
85: (x,y) = (-8.14372, 98.2145)
After 86 steps, the subject has the following location:
(x,y) = (-22.0369, 112.601)
 or
(m,a) = (114.737, 1.76406)
Average outward distance per step = 1.33416

2. Vector类：稍作修改

对于Vector类的头文件（程序清单11.13）和实现文件（程序清单11.14）进行修改，使其不再储存矢量的长度和角度，而是在magval()和angval()被调用时计算它们。
应保留公有接口不变（公有方法及其参数不变），但对私有部分（包括一些私有方法）和方法实现进行修改。然后，使用程序清单11.15对修改后的版本进行测试，结果应该与以前相同，因为Vecotr类的公有接口与原来相同。

代码：

vector.h：

#ifndef VECTOR_H
#define VECTOR_H
#include <iostream>

namespace VECTOR
{
    class Vector
    {
    public:
        enum Mode
        {
            RECT,
            POL
        };

    private:
        double x;
        double y;
        Mode mode;

        double set_mag();
        double set_ang();
        void set_x(double mag, double ang);
        void set_y(double mag, double ang);

    public:
        Vector();
        Vector(double n1, double n2, Mode from = RECT);
        void reset(double n1, double n2, Mode from = RECT);
        ~Vector();
        double xval() const { return x; };
        double yval() const { return y; };
        double magval() const;
        double angval() const;
        void polar_mode();
        void rect_mode();

        Vector operator+(const Vector &b) const;
        Vector operator-(const Vector &b) const;
        Vector operator-() const;
        Vector operator*(double n) const;

        friend Vector operator*(double n, const Vector &a);
        friend std::ostream &operator<<(std::ostream &os, const Vector &v);
    };

}
#endif

vector.cpp：

#include "vector.h"
#include <iostream>
#include <cmath>
using namespace std;

namespace VECTOR
{
    const double Rad_to_deg = 45.0 / atan(1.0);
    double Vector::set_mag()
    {
        double mag;
        mag = sqrt(x * x + y * y);
        return mag;
    }
    double Vector::set_ang()
    {
        double ang;
        if (x == 0 && y == 0)
            ang = 0.0;
        else
            ang = atan2(y, x);
        return ang;
    }
    void Vector::set_x(double mag, double ang)
    {
        x = mag * cos(ang);
    }
    void Vector::set_y(double mag, double ang)
    {
        y = mag * sin(ang);
    }
    Vector::Vector()
    {
        x = y = 0;
        mode = RECT;
    }
    Vector::Vector(double n1, double n2, Mode from)
    {
        mode = from;
        if (from == RECT)
        {
            x = n1;
            y = n2;
            set_mag();
            set_ang();
        }
        else if (from == POL)
        {
            double mag, ang;
            mag = n1;
            ang = n2 / Rad_to_deg;
            set_x(mag, ang);
            set_y(mag, ang);
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector()--";
            cout << "vector set to 0" << endl;
            x = y = 0.0;
            mode = RECT;
        }
    }
    void Vector::reset(double n1, double n2, Mode from)
    {
        mode = from;
        if (from == RECT)
        {
            x = n1;
            y = n2;
        }
        else if (from == POL)
        {
            double mag, ang;
            mag = n1;
            ang = n2 / Rad_to_deg;
            set_x(mag, ang);
            set_y(mag, ang);
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector()--";
            cout << "vector set to 0" << endl;
            x = y = 0.0;
            mode = RECT;
        }
    }
    Vector::~Vector()
    {
    }
    double Vector::magval() const
    {
        double mag;
        mag = sqrt(x * x + y * y);
        return mag;
    }

    double Vector::angval() const
    {
        double ang;
        if (x == 0.0 && y == 0.0)
            ang = 0.0;
        else
            ang = atan2(y, x);
        return ang;
    }

    void Vector::polar_mode()
    {
        mode = POL;
    }
    void Vector::rect_mode()
    {
        mode = RECT;
    }
    Vector Vector::operator+(const Vector &b) const
    {
        return Vector(x + b.x, y + b.y);
    }
    Vector Vector::operator-(const Vector &b) const
    {
        return Vector(x - b.x, y - b.y);
    }
    Vector Vector::operator-() const
    {
        return Vector(-x, -y);
    }
    Vector Vector::operator*(double n) const
    {
        return Vector(n * x, n * y);
    }
    Vector operator*(double n, const Vector &a)
    {
        return a * n;
    }
    ostream &operator<<(ostream &os, const Vector &v)
    {
        if (v.mode == Vector::RECT)
            os << "(x,y) = (" << v.x << ", " << v.y << ")";
        else if (v.mode == Vector::POL)

            os << "(m,a) = (" << v.magval() << ", " << v.angval() << ")";
        else
            os << "Vector object mode is invalid";
        return os;
    }
}

randwalk.cpp：

#include "vector.h"
#include <iostream>
#include <cstdlib> //rand(), srand() prototypes
#include <ctime>   //time() prototype
using namespace std;

int main()
{
    using VECTOR::Vector;
    srand(time(0));
    double direction;
    Vector step;
    Vector result(0.0, 0.0);
    unsigned long steps = 0;
    double target;
    double dstep;

    cout << "Enter target distance (q to quit): ";
    while (cin >> target)
    {
        cout << "Enter step length: ";
        if (!(cin >> dstep))
            break;
        while (result.magval() < target)
        {
            direction = rand() % 360;
            step.reset(dstep, direction, Vector::POL);
            result = result + step;
            steps++;
        }
        cout << "After " << steps << " steps, the subject has the following location:\n";
        cout << result << endl;
        result.polar_mode();
        cout << " or\n"
             << result << endl;
        cout << "Average outward distance per step = " << result.magval() / steps << endl;
        steps = 0;
        result.reset(0.0, 0.0);
        cout << "Enter target distance (q to quit): ";
    }
    cout << "Bye!\n";
    cin.clear();
    while (cin.get() != '\n')
        continue;

    system("pause");
    return 0;
}

运行结果：

3. 最低、最高和平均步数

代码：

vector.h和vector.cpp同11.1。

randwalk.cpp：

#include "vector.h"
#include <iostream>
#include <cstdlib> //rand(), srand() prototypes
#include <ctime>   //time() prototype
using namespace std;

int main()
{
    using VECTOR::Vector;
    srand(time(0));
    double direction;
    Vector step;
    Vector result(0.0, 0.0);
    unsigned long steps = 0;
    double target;
    double dstep;
    int N = 0;
    int max = 0, min = 100000, sum = 0;
    double average = 0.0;

    cout << "How many times do you want to test? ";
    cin >> N;
    for (int i = 0; i < N; i++)
    {
        cout << "Enter #"<<i+1<<" target distance: ";
        if (!(cin >> target))
            break;
        cout << "Enter #"<<i+1<<" step length: ";
        if (!(cin >> dstep))
            break;
        while (result.magval() < target)
        {
            direction = rand() % 360;
            step.reset(dstep, direction, Vector::POL);
            result = result + step;
            steps++;
        }
        cout << "# " << i + 1 << ": After " << steps << " the subject reach destination.\n";
        // cout << result << endl;
        // result.polar_mode();
        // cout << " or\n"
        //      << result << endl;
        // cout << "Average outward distance per step = " << result.magval() / steps << endl;
        if (steps > max)
            max = steps;
        if (steps < min)
            min = steps;
        sum += steps;
        steps = 0;
        result.reset(0.0, 0.0);
    }
    average = (double)sum / N;
    cout << "The max steps is: " << max << endl;
    cout << "The min steps is: " << min << endl;
    cout << "The average steps is: " << average << endl;
    cout << "Bye!\n";
    cin.clear();

    system("pause");
    return 0;
}

运行结果：

4. Time类：使用友元函数来实现所有的重载运算符

重新编写最后的Time类示例（程序清单11.10、程序清单11.11和程序清单11.12），使用友元函数来实现所有的重载运算符。

代码：

mytime.h：

#ifndef MYTIME_H
#define MYTIME_H
#include <iostream>
class Time
{
private:
    int hours;
    int minutes;

public:
    Time();
    Time(int h, int m = 0);
    void AddMin(int m);
    void AddHr(int h);
    void Reset(int h = 0, int m = 0);

    friend Time operator+(const Time &t1, const Time &t2);
    friend Time operator-(const Time &t1, const Time &t2);
    friend Time operator*(const Time &t, double mult);
    friend Time operator*(double m, const Time &t) { return t * m; }
    friend std::ostream &operator<<(std::ostream &os, const Time &t);
};

#endif

mytime.cpp：

#include "mytime.h"
#include <iostream>

Time::Time()
{
    hours = minutes = 0;
}
Time::Time(int h, int m)
{
    hours = h;
    minutes = m;
}
void Time::AddMin(int m)
{
    hours += m;
    hours += minutes / 10;
    minutes %= 60;
}
void Time::AddHr(int h)
{
    hours += h;
}
void Time::Reset(int h, int m)
{
    hours = h;
    minutes = m;
}

Time operator+(const Time &t1, const Time &t2)
{
    Time sum;
    sum.minutes = t1.minutes + t2.minutes;
    sum.hours = t1.hours + t2.hours + sum.minutes / 60;
    sum.minutes %= 60;
    return sum;
}
Time operator-(const Time &t1, const Time &t2)
{
    Time diff;
    int tot1, tot2;
    tot1 = t1.minutes + 60 * t1.hours;
    tot2 = t2.minutes + 60 * t2.hours;
    diff.hours = (tot2 - tot1) / 60;
    diff.minutes = (tot2 - tot1) % 60;
    return diff;
}
Time operator*(const Time &t, double mult)
{
    Time result;
    long totalminutes = t.hours * mult * 60 + t.minutes * mult;
    result.hours = totalminutes / 60;
    result.minutes = totalminutes % 60;
    return result;
}
std::ostream &operator<<(std::ostream &os, const Time &t)
{
    os << t.hours << " hours, " << t.minutes << " minutes";
    return os;
}

usetime.cpp：

#include "mytime.h"
#include <iostream>

int main()
{
    using std::cout;
    using std::endl;
    Time aida(3, 35);
    Time tosca(2, 48);
    Time temp;

    cout << "Aida and Tosca:\n";
    cout << aida << "; " << tosca << endl;
    temp = aida + tosca;
    cout << "Aida + Tosca: " << temp << endl;
    temp = aida * 1.17;
    cout << "Aida * 1.17: " << temp << endl;
    cout << "10.0 * Tosca: " << 10.0 * tosca << endl;

    system("pause");
    return 0;
}

运行结果：

5. Stonewt类：新增状态成员、重载运算符

重新编写Stonewt类（程序清单11.16和程序清单11.17），使它有一个状态成员，由该状态成员控制对象应转换为英石格式、整数磅格式还是浮点磅格式。重载<<运算符，使用它来替换show_stn()和show_lbs()方法。重载加法、减法和乘法运算符，以便可以对Stonewt值进行加、减、乘运算。编写一个使用所有类方法和友元的小程序，来测试这个类。

代码：

stonewt.h：

#ifndef STONEWT_H
#define STONEWT_H
#include <iostream>

class Stonewt
{
public:
    enum Format
    {
        STONE,
        INT_POUND,
        DOUBLE_POUND
    };

private:
    enum
    {
        Lbs_per_stn = 14
    };
    Format m_form;
    int stone;
    double pds_left;
    double pounds;

public:
    Stonewt(double lbs);
    Stonewt(int stn, double lbs);
    Stonewt();
    ~Stonewt();
    void SetFormat(Format form);
    Stonewt operator+(const Stonewt &s) const;
    Stonewt operator-(const Stonewt &s) const;
    Stonewt operator*(double n) const;
    friend Stonewt operator*(double m, const Stonewt &s) { return s * m; }
    friend std::ostream &operator<<(std::ostream &os, const Stonewt &s);
};

#endif

stonewt.cpp：

#include "stonewt.h"
#include <iostream>

Stonewt::Stonewt(double lbs)
{
    stone = int(lbs) / Lbs_per_stn;
    pds_left = int(lbs) % Lbs_per_stn + lbs - int(lbs);
    pounds = lbs;
    m_form = STONE;
}
Stonewt::Stonewt(int stn, double lbs)
{
    stone = stn;
    pds_left = lbs;
    pounds = stn * Lbs_per_stn + lbs;
    m_form = INT_POUND;
}
Stonewt::Stonewt()
{
    stone = pounds = pds_left = 0;
    m_form = DOUBLE_POUND;
}
Stonewt::~Stonewt()
{
}
void Stonewt::SetFormat(Format from)
{
    m_form = from;
}
Stonewt Stonewt::operator+(const Stonewt &s) const
{
    Stonewt sum;
    sum.pounds = pounds + s.pounds;
    sum.stone = int(sum.pounds) / Lbs_per_stn;
    sum.pds_left = int(sum.pounds) % Lbs_per_stn + sum.pounds - int(sum.pounds);
    return sum;
}
Stonewt Stonewt::operator-(const Stonewt &s) const
{
    Stonewt diff;
    diff.pounds = pounds - s.pounds;
    diff.stone = int(diff.pounds) / Lbs_per_stn;
    diff.pds_left = int(diff.pounds) % Lbs_per_stn + diff.pounds - int(diff.pounds);
    return diff;
}
Stonewt Stonewt::operator*(double n) const
{
    double mult;
    mult = pounds * n;
    return Stonewt(mult);
}
std::ostream &operator<<(std::ostream &os, const Stonewt &s)
{
    if (s.m_form == Stonewt::STONE)
    {
        os << s.stone << " stone, " << s.pds_left << " pounds\n";
    }
    else if (s.m_form == Stonewt::INT_POUND)
    {
        os << int(s.pounds) << " pounds\n";
    }
    else if (s.m_form == Stonewt::DOUBLE_POUND)
    {
        os << s.pounds << " pounds\n";
    }
    else
        os << "Stonewt state is invalid";
    return os;
}

stone.cpp：

#include "stonewt.h"
#include <iostream>
using namespace std;

int main()
{

    Stonewt incognito = 275;
    Stonewt wolfe(285.7);
    Stonewt taft(21, 8);

    cout << "The celebrity weighed " << incognito;    // STONE
    cout << "The detective weighed " << wolfe;        // STONE
    cout << "The President weighed " << taft << endl; // INT_POUND

    Stonewt tf(2);
    Stonewt sum, diff, mult;

    sum = incognito + tf;
    diff = wolfe - tf;
    mult = taft * 2;
    cout << "The result will display as double_pounds:\n";
    cout << "After dinner, the celebrity weighed ";
    sum.SetFormat(Stonewt::DOUBLE_POUND);
    cout << sum;
    cout << "After sport, the detective weighed ";
    diff.SetFormat(Stonewt::DOUBLE_POUND);
    cout << diff;
    cout << "Now,the President weighed ";
    mult.SetFormat(Stonewt::DOUBLE_POUND);
    cout << mult;

    system("pause");
    return 0;
}

运行结果：

6. Stonewt类：重载全部关系运算符

重新编写Stonewt类（程序清单11.16和程序清单11.17），重载全部6个关系运算符。运算符对pounds成员进行比较，并返回一个bool值。编写一个程序，它声明一个包含6个Stonewt对象的数组，并在数组声明中初始化前3个对象。然后使用循环来读取用于设置剩余3个数组元素的值。接着报告最小的元素、最大的元素以及大于或等于11英石的元素的数量（最简单的方法是创建一个Stonewt对象，并将其初始化为11英石，然后将其同其他对象进行比较）。

代码：

stonewt.h：

#ifndef STONEWT_H
#define STONEWT_H
#include <iostream>

class Stonewt
{
public:
    enum Format
    {
        STONE,
        INT_POUND,
        DOUBLE_POUND
    };

private:
    enum
    {
        Lbs_per_stn = 14
    };
    Format m_form;
    int stone;
    double pds_left;
    double pounds;

public:
    Stonewt(double lbs);
    Stonewt(int stn, double lbs);
    Stonewt();
    ~Stonewt();
    void SetFormat(Format form);
    // Stonewt operator+(const Stonewt &s) const;
    // Stonewt operator-(const Stonewt &s) const;
    // Stonewt operator*(double n) const;
    // friend Stonewt operator*(double m, const Stonewt &s) { return s * m; }
    friend bool operator>(const Stonewt &s1, const Stonewt &s2);
    friend bool operator<(const Stonewt &s1, const Stonewt &s2);
    friend bool operator>=(const Stonewt &s1, const Stonewt &s2);
    friend bool operator<=(const Stonewt &s1, const Stonewt &s2);
    friend bool operator==(const Stonewt &s1, const Stonewt &s2);
    friend bool operator!=(const Stonewt &s1, const Stonewt &s2);
    friend std::ostream &operator<<(std::ostream &os, const Stonewt &s);
};

#endif

stonewt.cpp：

#include "stonewt.h"
#include <iostream>

Stonewt::Stonewt(double lbs)
{
    stone = int(lbs) / Lbs_per_stn;
    pds_left = int(lbs) % Lbs_per_stn + lbs - int(lbs);
    pounds = lbs;
    m_form = STONE;
}
Stonewt::Stonewt(int stn, double lbs)
{
    stone = stn;
    pds_left = lbs;
    pounds = stn * Lbs_per_stn + lbs;
    m_form = INT_POUND;
}
Stonewt::Stonewt()
{
    stone = pounds = pds_left = 0;
    m_form = DOUBLE_POUND;
}
Stonewt::~Stonewt()
{
}
void Stonewt::SetFormat(Format from)
{
    m_form = from;
}
// Stonewt Stonewt::operator+(const Stonewt &s) const
// {
//     Stonewt sum;
//     sum.pounds = pounds + s.pounds;
//     sum.stone = int(sum.pounds) / Lbs_per_stn;
//     sum.pds_left = int(sum.pounds) % Lbs_per_stn + sum.pounds - int(sum.pounds);
//     return sum;
// }
// Stonewt Stonewt::operator-(const Stonewt &s) const
// {
//     Stonewt diff;
//     diff.pounds = pounds - s.pounds;
//     diff.stone = int(diff.pounds) / Lbs_per_stn;
//     diff.pds_left = int(diff.pounds) % Lbs_per_stn + diff.pounds - int(diff.pounds);
//     return diff;
// }
// Stonewt Stonewt::operator*(double n) const
// {
//     double mult;
//     mult = pounds * n;
//     return Stonewt(mult);
// }

bool operator>(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds > s2.pounds)
        return true;
    else
        return false;
}
bool operator<(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds < s2.pounds)
        return true;
    else
        return false;
}
bool operator>=(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds >= s2.pounds)
        return true;
    else
        return false;
}
bool operator<=(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds <= s2.pounds)
        return true;
    else
        return false;
}
bool operator==(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds == s2.pounds)
        return true;
    else
        return false;
}
bool operator!=(const Stonewt &s1, const Stonewt &s2)
{
    if (s1.pounds != s2.pounds)
        return true;
    else
        return false;
}
std::ostream &operator<<(std::ostream &os, const Stonewt &s)
{
    if (s.m_form == Stonewt::STONE)
    {
        os << s.stone << " stone, " << s.pds_left << " pounds\n";
    }
    else if (s.m_form == Stonewt::INT_POUND)
    {
        os << int(s.pounds) << " pounds\n";
    }
    else if (s.m_form == Stonewt::DOUBLE_POUND)
    {
        os << s.pounds << " pounds\n";
    }
    else
        os << "Stonewt state is invalid";
    return os;
}

stone.cpp：

#include "stonewt.h"
#include <iostream>
using namespace std;

int main()
{
    Stonewt s[6] = {275, 285.7, Stonewt(21, 8.0)};

    cout << "Enter the rest three Stonewt:\n";
    for (int i = 3; i < 6; i++)
    {
        double pounds;
        cout << "#" << i + 1 << ": ";
        cin >> pounds;
        s[i] = pounds;
    }

    Stonewt s_max = s[0], s_min = s[0], flag(11, 0.0);
    int count = 0;

    for (int i = 0; i < 6; i++)
    {
        cout << "#" << i + 1 << ": " << s[i] << endl;
        if (s[i] > s_max)
            s_max = s[i];
        if (s[i] < s_min)
            s_min = s[i];
        if (s[i] >= flag)
            count++;
    }

    cout << "The max is " << s_max;
    cout << "The min is " << s_min;
    if (count > 1)
        cout << "There are " << count << " members greater than or equal to 11 stones.\n";
    else
        cout << "There is " << count << " member greater than or equal to 11 stones.\n";

    system("pause");
    return 0;
}

运行结果：

7.

复数有两个部分组成：实数部分和虚数部分。复数的一种书写方式是：（3.0,4.0），其中，3.0是实数部分，4.0是虚数部分。假设a=(A,Bi),c=(C,Di)，则下面是一些复数运算。

• 加法：a+c=(A+C,(B+D)i)。
• 减法：a-c=(A-C,(B-D)i)。
• 乘法：a * c=(A*C-B * D,(A * D+B * C)i)。
• 乘法::x * c=(x * C,x * Di)，其中x为实数。
• 共轭：~a=(A,-Bi)。

请定义一个复数类，以便下面的程序可以使用它来获得正确的结果。

#include <iostream>
#include "complex0.h"
using namespace std;
 
int main(void)
{
	complex a(3.0, 4.0);
	complex c;
 
	cout << "Enter a complex number (q to quit):\n";
	while (cin >> c)
	{
		cout << "c is " << c << endl;
		cout << "complex conjugate is " << ~c << endl;
		cout << "a is " << a << endl;
		cout << "a + c is " << a + c << endl;
		cout << "a - c is " << a - c << endl;
		cout << "a * c is " << a * c << endl;
		cout << "2 * c is " << 2 * c << endl;
		cout << "Enter a complex number (q to quit):" << endl;
	}
	cout << "Done!" << endl;

	return 0;
}

注意。必须重载运算符<<和>>。标准C++使用头文件complex提供了比这个示例更广泛的复数支持，因此应将自定义的头文件命名为complex0.h，以免发生冲突。应尽可能使用const。
下面是该程序的运行情况。

Enter a complex number (q to quit):
real: 10
imaginary: 12
c is (10,12i)
complex conjugate is (10,-12i)
a is (3,4i)
a + c is (13,16i)
a - c is (-7,-8i)
a * c is (-18,76i)
2 * c is (20,24i)
Enter a complex number (q to quit):
real: q
Done!

请注意，经过重载后，cin>>c将提示用户输入实数和虚数部分。

代码：

complex0.h：

#ifndef COMPLEX0_H
#define COMPLEX0_H
#include <iostream>

class complex
{
private:
    double real;
    double imaginary;

public:
    complex();
    complex(const double r, const double i);
    ~complex();
    complex operator+(const complex &c) const;
    complex operator-(const complex &c) const;
    complex operator*(const complex &c) const;
    complex operator*(double x) const;
    complex operator~() const;
    friend complex operator*(double x, const complex &c) { return c * x; };
    friend std::ostream &operator<<(std::ostream &os, const complex &c);
    friend std::istream &operator>>(std::istream &is, complex &c);
};

#endif

complex0.cpp：

#include "complex0.h"
#include <iostream>

complex::complex()
{
    real = imaginary = 0.0;
}
complex::complex(const double r, const double i)
{
    real = r;
    imaginary = i;
}
complex::~complex()
{
}
complex complex::operator+(const complex &c) const
{
    complex sum;
    sum.real = real + c.real;
    sum.imaginary = imaginary + c.imaginary;
    return sum;
}
complex complex::operator-(const complex &c) const
{
    complex diff;
    diff.real = real - c.real;
    diff.imaginary = imaginary - c.imaginary;
    return diff;
}
complex complex::operator*(const complex &c) const
{
    complex mult;
    mult.real = real * c.real - imaginary * c.imaginary;
    mult.imaginary = real * c.imaginary + imaginary * c.real;
    return mult;
}
complex complex::operator*(double x) const
{
    complex mult;
    mult.real = real * x;
    mult.imaginary = imaginary * x;
    return mult;
}
complex complex::operator~() const
{
    return complex(real, -imaginary);
}
std::ostream &operator<<(std::ostream &os, const complex &c)
{
    os << "(" << c.real << "," << c.imaginary << "i)";
    return os;
}
std::istream &operator>>(std::istream &is, complex &c)
{
    std::cout << "real: ";
    if (is >> c.real)
    {
        std::cout << "imaginary: ";
        is >> c.imaginary;
    }

    return is;
}

main.cpp：

#include "complex0.h"
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
    complex a(3.0, 4.0);
    complex c;

    cout << "Enter a complex number (q to quit):\n";
    while (cin >> c)
    {
        cout << "c is " << c << endl;
        cout << "complex conjugate is " << ~c << endl;
        cout << "a is " << a << endl;
        cout << "a + c is " << a + c << endl;
        cout << "a - c is " << a - c << endl;
        cout << "a * c is " << a * c << endl;
        cout << "2 * c is " << 2 * c << endl;
        cout << "Enter a complex number (q to quit):" << endl;
    }
    cout << "Done!\n";

    system("pause");
    return 0;
}

运行结果：