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C++ Primer Plus 第十一章答案 使用类

2023-06-15 71
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简介： 只有聪明人才能看见的摘要～(￣▽￣～)~

复习题

#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
//11.8
//1
Stonewt operator*(double mult);//原型
Stonewt Stonewt::operator*(double mult) {
  return Stonewt(mult * pounds);
}
//2
成员函数是类定义的一部分，通过特定的对象来调用。成员函数可以隐式地访问调用对象的成员，
而无需使用成员运算符。友元函数不是类的组成部分，因此被称为直接函数调用。友元函数不能
隐式地访问类成员，必须将成员运算符用于作为参数传递的对象。可比较复习题1和4
//3
要访问私有成员，必须是友元，要访问公有成员，可以不是友元
//4
friend Stonewt operator*(double mult, const Stonewt& w);//原型
Stonewt operator*(double mult, const Stonewt& w) {//函数定义
  return Stonewt(mult * w.pounds);
}
//5
\sizeof\.\.*\::\ ? : \
\typeid\const_cast\dynamic_cast\reinterpret_cast\static_cast\
//6
这些运算符必须使用成员函数定义
//7
operator double()const { return mag; }

image.gif

practice 1

找不到程序清单复制粘贴，就很难受

//vect.h -- Vector class with <<,mode state
#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
#ifndef VECT_H_
#define VECT_H_
#include<iostream>
namespace VECTOR {
  class Vector {
  public:
    enum Mode{RECT,POL};
    //RECT for rectangular,POL for Polar modes
  private:
    double x;
    double y;
    double mag;
    double ang;
    Mode mode;
    //Private methods for setting values
    void set_mag();
    void set_ang();
    void set_x();
    void set_y();
  public:
    Vector();
    Vector(double n1, double n2, Mode form = RECT);
    void reset(double n1, double n2, Mode form = RECT);
    ~Vector();
    double xval() { return x; }
    double yval() { return y; }
    double magval() { return mag; }
    double angval() { return ang; }
    void polar_mode();
    void rect_mode();
    //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
//vect.cpp -- methods for the Vector class
#include<cmath>
#include"vect.h"
using std::sqrt;
using std::sin;
using std::cos;
using std::atan;
using std::atan2;
using std::cout;
namespace VECTOR {
  //compute degrees in one radian
  const double Rad_to_deg = 45.0 / atan(1.0);
  //should be about 57.2957795130823
  //private method
  //calculates magnitude from x and y
  void Vector::set_mag() 
  {
    mag = sqrt(x * x + y * y);
  }
  void Vector::set_ang() 
  {
    if (x == 0.0 && y == 0.0)
      ang = 0.0;
    else
      ang = atan2(y, x);
  }
  //set x from polar coordinate
  void Vector::set_x()
  {
    x = mag * cos(ang);
  }
  //set y from polar coordinate
  void Vector::set_y()
  {
    y = mag * sin(ang);
  }
  //public metohds
  Vector::Vector()
  {
    x = y = mag = ang = 0.0;
    mode = RECT;
  }
  //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, Mode form)
  {
    mode = form;
    if (form == RECT)
    {
      x = n1;
      y = n2;
      set_mag();
      set_ang();
    }
    else if (form == POL)
    {
      mag = n1;
      ang = n2;
      set_x();
      set_y();
    }
    else
    {
      cout << "Incorrent 3rd argument to Vector() -- ";
      cout << "Vector set to 0\n";
      x = y = mag = ang = 0.0;
      mode = RECT;
    }
  }
  //reset vector from rectangular coordinates if form is
  //RECT(the default) or else form polar coordinates if
  //form is POL
  void Vector::reset(double n1, double n2, Mode form)
  {
    mode = form;
    if (form == RECT)
    {
      x = n1;
      y = n2;
      set_mag();
      set_ang();
    }
    else if (form == POL)
    {
      mag = n1;
      ang = n2;
      set_x();
      set_y();
    }
    else
    {
      cout << "Incorrent 3rd argument to Vector() -- ";
      cout << "Vector set to 0\n";
      x = y = mag = ang = 0.0;
      mode = RECT;
    }
  }
  Vector::~Vector()
  {
  }
  void Vector::polar_mode()
  {
    mode = POL;
  }
  void Vector::rect_mode()
  {
    mode = RECT;
  }
  //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);
  }
  //multiply 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, Vector& a)
  {
    return a * n;
  }
  //display rectangular coordinate if mode is RECT
  //else display polar coordinates if mode is POL
  std::ostream& operator<<(std::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 * Rad_to_deg << ")";
    else
      os << "Vector object mode is invalid.";
    return os;
  }
}//end namespace VECTOR
//randwalk.cpp -- suing the Vector class
//compile with the vect.cpp file
#include<iostream>
#include<cstdlib>
#include<ctime>
#include"vect.h"
#include<fstream>
int main() {
  using namespace std;
  using namespace VECTOR;
  srand(time(0));
  double direction;//方向:角度
  Vector step;//创建类矢量:每一步
  Vector result(0, 0);//结果:累积矢量
  unsigned long steps = 0;//步数
  double target = 100;//目标距离
  double dstep = 20;//每一步长度
  ofstream fout;
  fout.open("jieguo.txt");
  fout << "Target Distance: " << target << ", Step Size: " << dstep << endl;
  fout << steps << ": " << result << endl;
  while (result.magval() < target)
  {
    direction = rand() % 360;
    step.reset(dstep, direction, Vector::POL);
    result = result + step;
    steps++;
    fout << steps << ": " << result << endl;
  }
  fout << "After " << steps << " steps,the subject "
    << "has the following location:\n";
  fout << result << endl;
  result.polar_mode();
  fout << " or " << endl << result << endl;
  fout << "Average outward distance per step = "
    << result.magval() / steps << endl;
  fout << "Bye!\n";
  return 0;
}

image.gif

运行结果如下：

image.gif编辑

practice 2

针对practice 1的答案做如下修改，因为不能存储mag和ang

1，因此要更改四个计算x,y,mag,ang的私有方法，前两个要返回double值以使用，后两个要传递两个double参数。

2，公有方法里的返回mag和ang值的内联函数magval(),angval()需要修改，在main里面会用到。

3，显然构造函数也需要对应的修改。

4，修改reset()，与带参数的构造函数一致。

5，最后修改<<运算符的重载函数，这里可能出现错误

E1086    对象含有与成员 函数 "VECTOR::Vector::angval" 不兼容的类型限定符。有两种可能

       1）const对象只能调用const函数

       2）const函数中不小心修改了类成员或者调用了非常量函数

因为要显示mag和ang用到了修改后的set_mag(),set_ang()，这两个函数进行了运算不是常量函数

所以去掉参数列表的const就可以了，注意原型的const也要去掉，不然就会有各种奇奇怪怪的错误

6，最后把randwalk.cpp的代码改成和程序清单11.15完全一样就可以了。

//vect.h -- Vector class with <<,mode state
#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
#ifndef VECT_H_
#define VECT_H_
#include<iostream>
namespace VECTOR {
  class Vector {
  public:
    enum Mode{RECT,POL};
    //RECT for rectangular,POL for Polar modes
  private:
    double x;
    double y;
    Mode mode;
    //Private methods for setting values
    double set_mag();
    double set_ang();
    double set_x(double mag,double ang);
    double set_y(double mag,double ang);
  public:
    Vector();
    Vector(double n1, double n2, Mode form = RECT);
    void reset(double n1, double n2, Mode form = RECT);
    ~Vector();
    double xval() { return x; }
    double yval() { return y; }
    double magval() { return set_mag(); }
    double angval() { return set_ang(); }
    void polar_mode();
    void rect_mode();
    //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, Vector& v);
  };
}//end namespace VECTOR
#endif
//vect.cpp -- methods for the Vector class
#include<cmath>
#include"vect.h"
using std::sqrt;
using std::sin;
using std::cos;
using std::atan;
using std::atan2;
using std::cout;
namespace VECTOR {
  //compute degrees in one radian
  const double Rad_to_deg = 45.0 / atan(1.0);
  //should be about 57.2957795130823
  //private method
  //calculates magnitude from x and y
  double Vector::set_mag()
  {
    return sqrt(x * x + y * y);
  }
  double Vector::set_ang()
  {
    if (x == 0.0 && y == 0.0)
      return 0.0;
    else
      return atan2(y, x);
  }
  //set x from polar coordinate
  double Vector::set_x(double mag, double ang)
  {
    return x = mag * cos(ang);
  }
  //set y from polar coordinate
  double Vector::set_y(double mag, double ang)
  {
    return y = mag * sin(ang);
  }
  //public metohds
  Vector::Vector()
  {
    x = y = 0.0;
    mode = RECT;
  }
  //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, Mode form)
  {
    mode = form;
    if (form == RECT)
    {
      x = n1;
      y = n2;
    }
    else if (form == POL)
    {
      set_x(n1,n2);
      set_y(n1,n2);
    }
    else
    {
      cout << "Incorrent 3rd argument to Vector() -- ";
      cout << "Vector set to 0\n";
      x = y = 0.0;
      mode = RECT;
    }
  }
  //reset vector from rectangular coordinates if form is
  //RECT(the default) or else form polar coordinates if
  //form is POL
  void Vector::reset(double n1, double n2, Mode form)
  {
    mode = form;
    if (form == RECT)
    {
      x = n1;
      y = n2;
    }
    else if (form == POL)
    {
      set_x(n1, n2);
      set_y(n1, n2);
    }
    else
    {
      cout << "Incorrent 3rd argument to Vector() -- ";
      cout << "Vector set to 0\n";
      x = y = 0.0;
      mode = RECT;
    }
  }
  Vector::~Vector()
  {
  }
  void Vector::polar_mode()
  {
    mode = POL;
  }
  void Vector::rect_mode()
  {
    mode = RECT;
  }
  //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);
  }
  //multiply 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, Vector& a)
  {
    return a * n;
  }
  //display rectangular coordinate if mode is RECT
  //else display polar coordinates if mode is POL
  std::ostream& operator<<(std::ostream& os, Vector& v)
  {
    if (v.mode == Vector::RECT)
      os << "(x,y) = (" << v.x << "," << v.y << ")";
    else if (v.mode == Vector::POL)
      os << "(m,a) = " << "(" << v.set_mag() << ", "
      << v.set_ang() * Rad_to_deg << ")";
    else
      os << "Vector object mode is invalid.";
    return os;
  }
}//end namespace VECTOR
//randwalk.cpp -- suing the Vector class
//compile with the vect.cpp file
#include<iostream>
#include<cstdlib>
#include<ctime>
#include"vect.h"
#include<fstream>
int main() {
  using namespace std;
  using namespace VECTOR;
  srand(time(0));
  double direction;//方向:角度
  Vector step;//创建类矢量:每一步
  Vector result(0, 0);//结果:累积矢量
  unsigned long steps = 0;//步数
  double target;//目标距离
  double dstep;//每一步长度
  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);
    cout << "Enter target distance (q to quit): ";
  }
  cout << "Bye!";
  cin.clear();
  while (cin.get() != '\n')
    continue;
  return 0;
}

image.gif

practice 3

这题还是用原来的vect.h和vect.cpp，所以就不重复发代码了，直接复制practice 1，和书上的程序清单完全一致，抄了我半天。

这里我把vect.h里面类声明里面的enum改成了enum class，因为一直有警告要求首选enum class，注意把后面的RECT,POL加上限定符Mode::

//randwalk.cpp -- suing the Vector class
//compile with the vect.cpp file
#include<iostream>
#include<cstdlib>
#include<ctime>
#include"vect.h"
#include<fstream>
int main() {
  using namespace std;
  using namespace VECTOR;
  srand(time(0));
  double direction;//方向:角度
  Vector step;//创建类矢量:每一步
  Vector result(0, 0);//结果:累积矢量
  unsigned long steps = 0;//步数
  double target;//目标距离
  double dstep;//每一步长度
  int N;//执行次数
  cout << "Enter target distance (q to quit): ";
  cin >> target;
  cout << "Enter step length: ";
  cin >> dstep;
  cout << "Enter the execution times: ";
  cin >> N;
  unsigned long max = 0;
  unsigned long min = 0;
  unsigned long total = 0;
  for (int i = 0; i < N; i++)
  {
    while (result.magval() < target)
    {
      direction = rand() % 360;
      step.reset(dstep, direction, Vector::Mode::POL);
      result = result + step;
      steps++;
    }
    if (i == 0)
      max = min = steps;
    else
    {
      if (steps > max)
        max = steps;
      if (steps < min)
        min = steps;
      total += steps;
    }
    steps = 0;
    result.reset(0.0, 0.0);
  }
  cout << "Report the result of tests: "
    << "The maximum steps: " << max << endl
    << "The minimum steps: " << min << endl
    << "The average steps: " << double(total)/N << endl;
  cout << "Bye!";
  return 0;
}

image.gif

practice 4

//mytime.h -- Time class with friends
#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
#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, const double n);
  friend  Time operator*(const double n, const Time& t)
  {
    return t * n;
  }
  friend std::ostream& operator<<(std::ostream& os, const Time& t);
};
#endif
//mytime.cpp -- implementing Time methods
#include"mytime.h"
Time::Time()
{
  hours = minutes = 0;
}
Time::Time(int h, int m)
{
  hours = h;
  minutes = m;
}
void Time::AddMin(int m)
{
  minutes += m;
  hours += minutes / 60;
  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 time;
  time.minutes = t1.minutes + t2.minutes;;
  time.hours = t1.hours + t2.hours + time.minutes / 60;
  time.minutes %= 60;
  return time;
}
Time operator-(const Time& t1, const Time& t2)
{
  Time time;
  int tot1, tot2;
  tot1 = t1.minutes + t1.hours * 60;
  tot2 = t2.minutes + t2.hours * 60;
  time.hours = (tot1 - tot2) / 60;
  time.minutes = (tot1 - tot2) % 60;
  return time;
}
Time operator*(const Time& t, double n)
{
  Time time;
  long totalminutes = t.hours * 60 * n + t.minutes * n;
  time.hours = totalminutes / 60;
  time.minutes = totalminutes % 60;
  return time;
}
std::ostream& operator<<(std::ostream& os, const Time& t)
{
  os << t.hours << " hours, " << t.minutes << " minutes";
  return os;
}
//usetime.cpp -- using the Time class
//compile with the mytime.cpp file
#include<iostream>
#include"mytime.h"
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;
  return 0;
}

image.gif

practice 5

//stonewt.h -- definition for the Stone class
#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
#ifndef STONEWT_H_
#define STONEWT_H_
#include<iostream>
class Stonewt {
public:
  enum class Mode { STN, PDS_INT, PDS };
private:
  enum { Lbs_per_stn = 14 };
  int stone;
  double pds_left;
  double pounds;
  int pds_int;
  Mode mode;
  void pds_stn(){
    stone = pounds / Lbs_per_stn;
    pds_left = pounds - stone * Lbs_per_stn;
  }
  void pds_pdsint() {
    pds_int = int(pounds);
  }
  void stn_pds() {
    pounds = stone * Lbs_per_stn + pds_left;
  }
public:
  Stonewt(double pds);
  Stonewt(int stn, double pdsl);
  Stonewt();
  ~Stonewt();
  Stonewt operator + (const Stonewt & s)const;
  Stonewt operator - (const Stonewt & s)const;
  Stonewt operator * (double mul)const;
  void mode_STN() { mode = Mode::STN; }
  void mode_PDS() { mode = Mode::PDS; }
  void mode_PDS_INT() { mode = Mode::PDS_INT; }
  friend Stonewt operator*(double mult, const Stonewt& s)
  {
    return s * mult;
  }
  friend std::ostream& operator<<(std::ostream& os, const Stonewt& s);
};
#endif
//stonewt.cpp -- implementing Stonewt methods
#include"stonewt.h"
#include<iostream>
Stonewt::Stonewt(double pds)
{
  pounds = pds;
  pds_stn();
  pds_pdsint();
  mode = Mode::PDS;
}
Stonewt::Stonewt(int stn, double pdsl)
{
  stone = stn;
  pds_left = pdsl;
  stn_pds();
  pds_pdsint();
  mode = Mode::STN;
}
Stonewt::Stonewt() {
  pounds = stone = pds_left = 0;
  pds_int = 0;
  mode = Mode::PDS;
}
Stonewt::~Stonewt(){}
Stonewt Stonewt::operator + (const Stonewt& s)const
{
  Stonewt swt;
  swt.pounds = pounds + s.pounds;
  return Stonewt(swt.pounds);
}
Stonewt Stonewt::operator - (const Stonewt& s)const
{
  Stonewt swt;
  swt.pounds = pounds - s.pounds;
  return Stonewt(swt.pounds);
}
Stonewt Stonewt::operator * (double mult)const
{
  Stonewt swt;
  swt.pounds = pounds * mult;
  return Stonewt(swt.pounds);
}
std::ostream& operator<<(std::ostream& os, const Stonewt& s)
{
  if (s.mode == Stonewt::Mode::PDS)
    os << "Mode: PDS: " << s.pounds << " pounds";
  else if (s.mode == Stonewt::Mode::STN)
    os << "Mode: STN: " << s.stone << " stones, " << s.pds_left << "pounds";
  else if (s.mode == Stonewt::Mode::PDS_INT)
    os << "Mode: PDS_INT: " << s.pds_int << " pounds";
  else
    os << "The mode of Stonewt is wrong!";
  return os;
}
//main.cpp
#include<iostream>
#include"stonewt.h"
int main()
{
  using std::cout;
  using std::endl;
  Stonewt s1;
  Stonewt s2(321.123);
  Stonewt s3(10, 12.5);
  cout << s1 << endl << s2 << endl << s3 << endl;
  cout << "s2-s3= " << s2 - s3 << endl;
  cout << "s2+s3= " << s2 + s3 << endl;
  s1 = s3 * 13.5;
  cout << "s3*13.5= " << s1 << endl;
  s1 = 13.5 * s3;
  s1.mode_PDS_INT();
  cout << "13.5*s2= " << s1 << endl;
  s1.mode_STN();
  cout << "13.5*s2= " << s1 << endl;
  return 0;
}

image.gif

image.gif编辑

practice 6

不能怪我懒，主要是抄代码实在太费时间了，所以直接用上一题的代码好了

贴太多代码看着都麻烦，所以只贴增加的一部分

//add to stonewt.h
    bool operator>(const Stonewt& s);
  bool operator>=(const Stonewt& s);
  bool operator<(const Stonewt& s);
  bool operator<=(const Stonewt& s);
  bool operator==(const Stonewt& s);
  bool operator!=(const Stonewt& s);
//add to stonewt.cpp
bool Stonewt::operator>(const Stonewt& s)
{
  if (pounds > s.pounds)
    return true;
  else return false;
}
bool Stonewt::operator>=(const Stonewt& s)
{
  if (pounds >= s.pounds)
    return true;
  else return false;
}
bool Stonewt::operator<(const Stonewt& s)
{
  if (pounds < s.pounds)
    return true;
  else return false;
}
bool Stonewt::operator<=(const Stonewt& s)
{
  if (pounds <= s.pounds)
    return true;
  else return false;
}
bool Stonewt::operator==(const Stonewt& s)
{
  if (pounds == s.pounds)
    return true;
  else return false;
}
bool Stonewt::operator!=(const Stonewt& s)
{
  if (pounds != s.pounds)
    return true;
  else return false;
}
//main.cpp
#include<iostream>
#include"stonewt.h"
int main()
{
  using std::cout;
  using std::cin;
  using std::endl;
  Stonewt arr_s[6] = { 12.3,14.5,17.8 };
  Stonewt standard(11);
  for (int i = 0; i < 3; i++) {
    cout << "Enter three number to construct Stonewt:\n";
    cout << "#" << i + 3 << ": ";
    double pds;
    cin >> pds;
    arr_s[i + 3] = Stonewt(pds);
  }
  for (int i = 0; i < 6; i++) {
    cout << "arr_s[" << i << "]: " << arr_s[i] << endl;
  }
  int max = 0;
  int min = 0;
  int n = 0;
  for (int i = 0; i < 6; i++) {
    if (arr_s[max] < arr_s[i])
      max = i;
    if (arr_s[min] > arr_s[i])
      min = i;
    if (arr_s[i] >= standard)
      n++;
  }
  cout << "The heaviest is arr_s[" << max << "]\n"
    << "The lightest is arr_s[" << min << "]\n"
    << "The number of Stonewts not ligther than 11 pounds is " << n << endl;
  return 0;
}

image.gif

practice 7

这题我在自定义构造函数前没有用explicit，而且第二个参数是有默认参数，但是重载*的函数中2*c的函数我写了一个return c*2;   它不能自动转换，必须加（complex），就很奇怪，有没有懂的评论一下

//complex0.h
#pragma once//避免此头文件被包含多次，和#ifndef的作用类似
#ifndef COMPLEX0_H_
#define COMPLEX0_H_
#include<iostream>
class complex {
private:
  double real;
  double imaginary;
public:
  complex();
  complex(double rl, double imgnr = 0);
  complex operator+(const complex& c)const;
  complex operator-(const complex& c)const;
  complex operator*(const complex& c)const;
  complex operator~()const;
  friend complex operator*(double n,const complex& c);
  friend std::istream& operator>>(std::istream& os, complex& c);
  friend std::ostream& operator<<(std::ostream& os, const complex& c);
};
#endif
//complex0.cpp
#include"complex0.h"
complex::complex() {
  real = imaginary = 0.0;
}
complex::complex(double rl, double imgnr) {
  real = rl;
  imaginary = imgnr;
}
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 sub;
  sub.real = real - c.real;
  sub.imaginary = imaginary - c.imaginary;
  return sub;
}
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~()const {
  complex conjugate;
  conjugate.real = real;
  conjugate.imaginary = imaginary;
  return conjugate;
}
complex operator*(double n, const complex& c) {
  return c * n;
}
std::istream& operator>>(std::istream& is, complex& c) {
  std::cout << "real: ";
  is >> c.real;
  if (is) {
    std::cout << "imaginary: ";
    is >> c.imaginary;
  }
  return is;
}
std::ostream& operator<<(std::ostream& os, const complex& c) {
  os << "(" << c.real << "," << c.imaginary << "i)";
  return os;
}
//main.cpp
#include<iostream>
#include"complex0.h"
int main() {
  using std::cout;
  complex a(3.0, 4.0);
  complex c;
  cout << "Enter a complex number (q to quit): \n";
  while (std::cin >> c)
  {
    cout << "c is " << c << '\n';
    cout << "complex  conjugate is " << ~c << '\n';
    cout << "a is " << a << '\n';
    cout << "a + c is " << a + c << '\n';
    cout << "a - c is " << a - c << '\n';
    cout << "a * c is " << a * c << '\n';
    cout << "2 * c is " << 2 * c << '\n';
    cout << "Enter a complex number (q to quit):\n";
  }
  cout << "Done!\n";
  return 0;
}

image.gif

为了搞清楚，我又双叒叕把（complex）去掉了，结果居然运行成功了

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