1 # ifndef VECTOR_H_
 2 # define VECTOR_H_
 3 # include "iostream"
 4
 5 namespace VECTOR //注意，这里对这个类定义了名称空间，实际上，在写自己的类时，也应该定义自己的名称空间
 6 {
 7     class Vector
 8     {
 9     public:
10         enum Mode{RECT,POL};//因为这个量需要用户自己去设定
11     private:           //注意：私有成员（无论是函数还是变量）只能被类内部成员访问
12         double x;
13         double y;
14         double mag;
15         double ang;
16         Mode mode;
17
18         void set_mag();
19         void set_ang();
20         void set_x();
21         void set_y();   //体会将这些函数放在这里的用意!!
22     public:             //共有成员可以被所有访问！！理解这个意思
23         Vector();//构造函数
24         Vector(double n1,double n2,Mode form = RECT);//注意，这里有默认参数
25         void reset(double n1, double n2, Mode form = RECT);
26         ~Vector();//析构函数
27         double xval() const{ return x; }
28         double yval() const{ return y; }
29         double magval() const{ return mag; }
30         double angval() const{ return ang; }
31         void polar_mode();
32         void rect_mode();
33
34         Vector operator+(const Vector &b) const;
35         Vector operator-(const Vector &b) const;
36         Vector operator-() const;
37         Vector operator*(double n) const;
38
39         friend Vector operator*(double n, const Vector &a);//注意这里采用了友元函数的做法，应该显示包含所有参数
40         friend std::ostream & operator<<(std::ostream &os, const Vector & v);//昨天没有思考返回引用是否存在问题？？？因为局部变量被销毁的问题
41     };
42
43 }
44 # endif

  1 # include"cmath"  //从下文的调用方法来看，这里应该是函数库，而不是类库
  2 # include "vector.h"
  3 using std::sqrt;   //注意 std 包含了很多
  4 using std::sin;
  5 using std::cos;
  6 using std::atan;
  7 using std::atan2;
  8 using std::cout;
  9
 10 namespace VECTOR  //名称空间的意义是很有必要的
 11 {
 12     const double Rad_to_deg = 45.0 / atan(1.0);
 13     void Vector::set_ang()
 14     {
 15         mag = sqrt(x*x + y*y); //求极长
 16     }
 17
 18     void Vector::set_ang()
 19     {
 20         if (x == 0.0  && y == 0.0)
 21             ang = 0.0;
 22         else
 23             ang = atan2(y, x);//求极角
 24     }
 25
 26     void Vector::set_x() //这些是私有函数
 27     {
 28         x = mag*cos(ang);//私有函数可以访问私有变量表明私有成员也可以相互访问
 29     }
 30
 31     void Vector::set_y()
 32     {
 33         y = mag*sin(ang);
 34     }
 35
 36     Vector::Vector()
 37     {
 38         x = y = mag = ang = 0.0;
 39         mode = RECT;
 40     }
 41
 42     Vector::Vector(double n1, double n2, Mode form)
 43     {
 44         mode  = form;
 45         if (form == RECT)
 46         {
 47             x = n1;
 48             y = n2;
 49             set_mag();//访问了私有成员
 50             set_ang();//体会这里的设计思想
 51         }
 52         else if (form == POL)
 53         {
 54             mag = n1;
 55             ang = n2;
 56             set_x();
 57             set_y();
 58         }
 59         else
 60         {
 61             cout << "Incorrect 3rd argument to Vector()--";
 62             cout << "vector set to 0\n";
 63             x = y = mag = ang = 0.0;
 64             mode =RECT;
 65         }
 66     }
 67     void Vector::reset(double n1, double n2, Mode form)
 68     {
 69         mode = form;
 70         if (form = RECT)
 71         {
 72             x = n1;
 73             y = n2;
 74             set_mag();
 75             set_ang();
 76         }
 77         else if (form = POL)
 78         {
 79             mag = n1;
 80             ang= n2;
 81             set_x();
 82             set_y();
 83         }
 84         else
 85         {
 86             cout << "Incorrect 3rd argument to Vector()--";
 87             cout << "vector set to 0\n";
 88             x = y = mag = ang = 0.0;
 89             mode = RECT;
 90         }
 91     }
 92     Vector::~Vector()//
 93     {
 94
 95     }
 96
 97     void Vector::polar_mode()
 98     {
 99         mode = POL;
100     }
101
102     void Vector::rect_mode()
103     {
104         mode = RECT;
105     }
106
107     Vector Vector::operator+(const Vector &b) const
108     {
109         return Vector(x + b.x, y + b.y);
110     }
111
112     Vector Vector::operator-(const Vector &b) const
113     {
114         return Vector(x - b.x, y - b.y);
115     }
116
117     Vector Vector::operator-() const
118     {
119         return Vector(-x, -y);
120     }
121 

        Vector Vector::operator*(double n) const

        {          return(n*x,x*y)        }

122     Vector operator*(double n, const Vector & a)
123     {
124         return a*n; //注意，虽然这里进行了返回，但并没有结束，而是继续调用了成员函数，
125     }
126
127     std::ostream & operator<<(std::ostream & os, const Vector & v)
128     {
129         if (v.mode == Vector::RECT)
130             os << "(x,y) = (" << v.x << "," << v.y << ")";
131         else if (v.mode == Vector::POL)
132         {
133             os << "(m,a) = (" << v.mag << "," << v.ang + Rad_to_deg << ")";
134         }
135         else
136             os << "Vector object mode is invalid";
137     }
138 }