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C++ Primer Plus（第五版）第11章编程题答案

C/C++ 编程 2018/11/18

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1.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，用步号进行标示。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。

#include

#include

#include

#include

#include “vector.h”
using namespace std;
using VECTOR::Vector;
int main() {
ofstream outFile;
outFile.open(“exercise1.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)
{
direction = rand() % 360;
step.set(dstep, direction, ‘p’);
result = result + step;
outFile << steps << “: (x,y) = “ << “(“ << step.xval() << “, “ << step.yval() << “)” << endl;
steps++;
}
outFile << “After “ << steps << “ steps, the subject “
“has the following location:\\n”;
outFile << “(x,y)=” << result << endl;
result.polar_mode();
outFile << “ or\\n” << result << endl;
outFile << “Average outward distance per step = “
<< result.magval() / steps << endl;
outFile << “====================================================”<<endl;
outFile << “COPYRIGHT 2018 WWW.YUSHUAI.XYZ” << endl;
steps = 0;
result.set(0.0, 0.0);
cout << “Enter target distance (q to quit): “;
}
outFile.close();
cout << “Bye~” << endl;
system(“pause”);
return 0;
}

2.对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，使其不再存储矢量的长度和角度，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Vector类的公有接口与原来相同。 vector.h

// vect.h – Vector class with <<, mode state

#ifndef VECTOR_H_

#define VECTOR_H_

#include
namespace VECTOR
{
class Vector
{
private:
double x; // horizontal value
double y; // vertical value
char mode; // ‘r’ = rectangular, ‘p’ = polar
// private methods for setting values
void set_x(double mag, double ang);
void set_y(double mag, double ang);
public:
Vector();
Vector(double n1, double n2, char form = ‘r’);
void set(double n1, double n2, char form = ‘r’);
~Vector();
double xval() const { return x; } // report x value
double yval() const { return y; } // report y value
double magval() const { return sqrt(x x + y y); } // report magnitude
double angval() const// report angle
{
if (x == 0.0 && y == 0.0)
return 0.0;
else
return atan2(y, x);
}

    void polar_mode();                    // set mode to 'p'
    void rect_mode();                     // set mode to 'r'
                                          // operator overloading
    Vector operator+(const Vector & b) const;
    Vector operator-(const Vector & b) const;
    Vector operator-() const;
    Vector operator*(double n) const;
    // friends
    friend Vector operator*(double n, const Vector & a);
    friend std::ostream & operator<<(std::ostream & os, const Vector & v);
};

} // end namespace VECTOR

#endif

#pragma once

vector.cpp

#include

#include “vector.h” // includes
using std::sqrt;
using std::sin;
using std::cos;
using std::atan2;
using std::cout;

namespace VECTOR
{

const double Rad\_to\_deg = 57.2957795130823;

// private methods
// calculates magnitude from x and y
// set x from polar coordinate
void Vector::set_x(double mag, double ang)
{
    x = mag * cos(ang);
}

// set y from polar coordinate
void Vector::set_y(double mag, double ang)
{
    y = mag * sin(ang);
}

// public methods
Vector::Vector()             // default constructor
{
    x = y = 0.0;
    mode = 'r';
}

// construct vector from rectangular coordinates if form is r
// (the default) or else from polar coordinates if form is p
Vector::Vector(double n1, double n2, char form)
{
    mode = form;
    if (form == 'r')
    {
        x = n1;
        y = n2;
    }
    else if (form == 'p')
    {
        set_x(n1, n2);
        set_y(n1, n2);
    }
    else
    {
        cout << "Incorrect 3rd argument to Vector() -- ";
        cout << "vector set to 0\\n";
        x = y = 0.0;
        mode = 'r';
    }
}

// set vector from rectangular coordinates if form is r (the
// default) or else from polar coordinates if form is p
void Vector::set(double n1, double n2, char form)
{
    mode = form;
    if (form == 'r')
    {
        x = n1;
        y = n2;
    }
    else if (form == 'p')
    {
        set_x(n1, n2);
        set_y(n1, n2);
    }
    else
    {
        cout << "Incorrect 3rd argument to Vector() -- ";
        cout << "vector set to 0\\n";
        x = y = 0.0;
        mode = 'r';
    }
}

Vector::~Vector()    // destructor
{
}

void Vector::polar_mode()    // set to polar mode
{
    mode = 'p';
}

void Vector::rect_mode()     // set to rectangular mode
{
    mode = 'r';
}

// operator overloading
// add two Vectors
Vector Vector::operator+(const Vector & b) const
{
    return Vector(x + b.x, y + b.y);
}

// subtract Vector b from a
Vector Vector::operator-(const Vector & b) const
{
    return Vector(x - b.x, y - b.y);
}

// reverse sign of Vector
Vector Vector::operator-() const
{
    return Vector(-x, -y);
}

// multiple vector by n
Vector Vector::operator*(double n) const
{
    return Vector(n * x, n * y);
}

// friend methods
// multiply n by Vector a
Vector operator*(double n, const Vector & a)
{
    return a * n;
}

// display rectangular coordinates if mode is r,
// else display polar coordinates if mode is p
std::ostream & operator<<(std::ostream & os, const Vector & v)
{
    if (v.mode == 'r')
        os << "(x,y) = (" << v.x << ", " << v.y << ")";
    else if (v.mode == 'p')
    {
        os << "(m,a) = (" << v.magval() << ", "
            << v.angval() * Rad\_to\_deg << ")";
    }
    else
        os << "Vector object mode is invalid";
    return os;
}

} // end namespace VECTOR

3.修改程序清单11.15，使之报告N次测试中的最高、最低和平均步数（其中N是用户输入的整数），而不是报告每次测试的结果。

#include

#include

#include

#include “vector.h”
using namespace std;
using VECTOR::Vector;
int main() {
srand(time(0));
double direction;
Vector step;
Vector result(0.0, 0.0);
unsigned long steps = 0;
double target;
double dstep;
unsigned long max = 0;
unsigned long min = 999;
double avg = 0;
int N;
cout << “请输入测试的次数：N=”;
cin >> N;
cout << “第一次：” << endl;
int i;
for (i = 0; i < N; i++)
{
cout << “Enter target distance(ONLY ENTER NUMBER): “;
cin >> target;
cout << “Enter step length: “;
if (!(cin >> dstep))
break;
while (result.magval() < target)
{
direction = rand() % 360;
step.set(dstep, direction, ‘p’);
result = result + step;
steps++;
}
if (max < steps)
max = steps;
if (min > steps)
min = steps;
avg += steps;
result.polar_mode();
steps = 0;
result.set(0.0, 0.0);
}
avg /= N;
cout << “max: “ << max << endl << “min: “ << min << endl << “average: “ << avg << endl;
cout << “Bye~”;
system(“pause”);
return 0;
}

4.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。 mytime3.h

#pragma once

#ifndef MYTIME3_H_

#define MYTIME3_H_

#include
using namespace std;
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 n);
friend Time operator(double m, const Time & t) { return t*m; }
friend ostream & operator<<(ostream & os, const Time & t);
};

#endif // !MYTIME_H_

mytime3.cpp

#include

#include “mytime3.h”
using namespace std;
Time::Time() {
hours = minutes = 0;

}
Time::Time(int h, int m) {
hours = h;
minutes = m;

}
void Time::AddMin(int m) {
minutes += m;
hours += minutes / 0;
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 = t2.minutes + 60 t2.hours;
tot2 = t1.minutes + 60 t1.hours;
diff.minutes = (tot2 - tot1) % 60;
diff.hours = (tot2 - tot1) / 60;
return diff;

}

Time operator(const Time &t, double n) {
Time result;
long totalminutes = t.hours\n * 60 + t.minutes*n;
result.hours = totalminutes / 60;
result.minutes = totalminutes % 60;
return result;
}

ostream & operator<<(ostream & os, const Time & t) {
os << t.hours << “ Hours, “ << t.minutes << “ minutes.”;
return os;
}

usetime3.cpp

#include

#include”mytime3.h”
using namespace std;
int main() {
Time aida(3, 35);
Time tosca(2, 48);
Time temp;
cout << “Aida and Tosca:\\n”;
cout << aida << “;” << tosca << endl;
temp = aida + tosca;
temp = aida1.17;
cout << “Aida1.17: “ << temp << endl;
cout << “10*Tosca: “ << 10 * tosca << endl;

system("pause");
return 0;

}

5.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。 stonewt.h

// stonewt.h – definition for the Stonewt class

#ifndef STONEWT_H_

#define STONEWT_H_
class Stonewt
{
private:
enum {Lbs_per_stn = 14}; // pounds per stone
int stone; // whole stones
double pds_left; // fractional pounds
double pounds; // entire weight in pounds
public:
Stonewt(double lbs); // constructor for double pounds
Stonewt(int stn, double lbs); // constructor for stone, lbs
Stonewt(); // default constructor
~Stonewt();
void show_lbs() const; // show weight in pounds format
void show_stn() const; // show weight in stone format
};

#endif

stonewt.cpp

// stonewt.cpp – Stonewt methods

#include
using std::cout;

#include “stonewt.h”

// construct Stonewt object from double value
Stonewt::Stonewt(double lbs)
{
stone = int (lbs) / Lbs_per_stn; // integer division
pds_left = int (lbs) % Lbs_per_stn + lbs - int(lbs);
pounds = lbs;
}

// construct Stonewt object from stone, double values
Stonewt::Stonewt(int stn, double lbs)
{
stone = stn;
pds_left = lbs;
pounds = stn * Lbs_per_stn +lbs;
}

Stonewt::Stonewt() // default constructor, wt = 0
{
stone = pounds = pds_left = 0;
}

Stonewt::~Stonewt() // destructor
{
}

// show weight in stones
void Stonewt::show_stn() const
{
cout << stone << “ stone, “ << pds_left << “ pounds\\n”;
}

// show weight in pounds
void Stonewt::show_lbs() const
{
cout << pounds << “ pounds\\n”;
}

stone.cpp

// stone.cpp – user-defined conversions
// compile with stonewt.cpp

#include
using std::cout;

#include “stonewt.h”
void display(const Stonewt & st, int n);
int main()
{
Stonewt pavarotti = 260; // uses constructor to initialize
Stonewt wolfe(285.7); // same as Stonewt wolfe = 285.7;
Stonewt taft(21, 8);

cout << "The tenor weighed ";
pavarotti.show_stn();
cout << "The detective weighed ";
wolfe.show_stn();
cout << "The President weighed ";
taft.show_lbs();
pavarotti = 265.8;       // uses constructor for conversion
taft = 325;      
cout << "After dinner, the tenor weighed ";
pavarotti.show_stn();
cout << "After dinner, the President weighed ";
taft.show_lbs();
display(taft, 2);
cout << "The wrestler weighed even more.\\n";
display(422, 2);
cout << "No stone left unearned\\n";
system("pause");
return 0;

}

void display(const Stonewt & st, int n)
{
for (int i = 0; i < n; i++)
{
cout << “Wow! “;
st.show_stn();
}
}

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）。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。 （……代码省略……） 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。 请注意，经过重载后，cin>>c将提示用户输入实数和虚数部分。 complex0.h

#pragma once

#include

#ifndef COM0_H_
using namespace std;
class complex {
double a;
double b;
public:
complex();
complex(double x, double y);
~complex();
complex operator+(const complex & t) const;
complex operator-(const complex & t) const;
friend complex operator(const complex & t,double n);//Êý³Ë
friend complex operator(const complex & t1, const complex & t2);
friend complex operator~(const complex & t);
friend ostream & operator<<(ostream & os, const complex & c);
friend istream & operator >> (istream &in, complex &c);

};

#endif // !COM0_H_

complex0.cpp

#include “complex0.h”

#include
complex::complex() {
a = 0;
b = 0;
}
complex::complex(double x, double y) {
a = x;
b = y;

}
complex::~complex() {}
complex complex::operator+(const complex & t) const
{

complex sum;
sum.a = a + t.a;
sum.b = b + t.b;
return sum;

}
complex complex::operator-(const complex & t) const
{
complex diff;
diff.a = a - t.a;
diff.b = b - t.b;
return diff;

}
complex operator(const complex & t, double n) //Êý³Ë
{
return complex((t.a)\n, (t.b)*n);

}

complex operator(const complex & t1, const complex & t2)
{
return complex((t1.a\t2.a - t1.b*t2.b), (t1.a*t2.b + t1.b*t2.a));

}
complex operator~(const complex & t)
{
return complex(t.a, (-1.0)*t.b);

}
ostream & operator<<(ostream & os, const complex & c)
{
os << “(“ << c.a << “,” << c.b << “!” << “)”;
return os;

}
istream & operator >> (istream &in, complex &c)
{
in >> c.a >> c.b;
return in;
}

备注： 操作系统：Windows 10 x64(1803) 编译器：Microsoft Visual Studio 2015

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