酒鬼随机漫步（一个矢量类）

摘要: 阅读全文

这是一个定义的一个矢量类， 然后用矢量类模拟一个酒鬼的随机漫步

问题很简单， 实现也不麻烦， 但是这个小程序却可以呈现出许多语法知识。而且代码风格也不错，因此保存在了这篇博客中。

 

建议：

       1. 类的声明以及函数的声明放到一个文件夹内， 并且在一些必要的地方加上注释！

　　 2. 函数的实现放到另一个文件内。

       3. 将程序要具体解决的问题放到另外的一个文件里。（详见代码！）

好处： 把类的接口和实现细节分离开， 易于更改某个函数的功能。

          把函数的声明和定义分开， 提高代码可读性。

          把类的声明和定义 与 要解决的问题分开， 提高，类的重用性！

                                         定义类（声明类内的函数）

// vect.h -- Vector class with <<, mode state
#ifndef VECTOR_H_
#define VECTOR_H_
#include <iostream>
namespace VECTOR
{
    class Vector
    {
    public:
        enum Mode{RECT, POL};
        // RECT for rectangular, POL for Polar modes
    private:
        double x;        // horizontal value
        double y;        // vertical value
        double mag;      // length of vector in degrees
        double ang;// direction of vector in degrees
           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() const {return x; }        // report x value
        double yval() const {return y; }        // report y value
        double magval() const {return mag; }    // report magnitude
        double angval() const {return ang; }    // report angle
        void polar_mode();                      // set mode to POL
        void rect_mode();                       // set mode to RECT
        // 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

 上面代码涵盖了许多关于类的基础知识:  名称空间与作用域 ，  实现类内部常量的方法，  构造函数， 析构函数， 运算符重载， 友元函数, 关于多种实现方法等。

PS： 实现类内部常量的方法： （1）枚举类型。 （2） static const int  常量

        运算符重载： 注意操作数的顺序。

                                           

                                                           函数定义

// vect.cpp -- methods for the Vector class 
#include <cmath>
#include "vect.h"  // include <iostream>
using std::sqrt;
using std::sin;
using std::cos;
using std::atan;
using std::atan2;
using std::cout;

namespace VECTOR
{
    // compute degree in one radian
    const double Rad_to_deg = 45.0/atan(1.0);
    // should be about 57.2957795130823

    // private methods
    // calculate 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 coodinate
    void Vector::set_y()
    {
        y = mag * sin(ang);
    }
    // public methods
    Vector::Vector() // default constructor
    {
        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/Rad_to_deg;
            set_x();
            set_y();
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector() --";
            cout << "vector set to 0.0";
            mode = RECT;
        }
    }

    // reset vector from rectangular coodinates 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/Rad_to_deg;
            set_x();
            set_y();
        }
        else
        {
            cout << "Incorrect 3rd argument to Vector() -- ";
            cout <<"vector set to 0.0
";
            x = y = mag = ang = 0.0;
            mode = RECT;
        }
    }

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

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

    void Vector::rect_mode()// set to rectangular 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, const Vector & a)
    {
        return a * n;
    }

    //display rectangular coordinates 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

                                                           具体解决的问题

// randwalk.cpp -- using the Vector class
// compile with the vect.cpp file
#include <iostream>
#include <cstdlib> // rand(), srand() pototypes
#include <ctime>   // time() pototype
#include "vect.h"

int main()
{
    using namespace std;
    using VECTOR::Vector;
    srand(time(0));   // seed random-number generator
    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:
";
        cout << result <<endl;
        result.polar_mode();
        cout << "or
" << 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!
";
    cin.clear();
    while(cin.get() != '
')
        continue;
    return 0;
}

二。一个简易的string类。

锻炼内容：

            拷贝构造函数（深拷贝与浅拷贝）

            重载赋值运算符（深赋值）

            许多的细节与技巧！

类的声明

//sting1.h -- fixed and augmented string class definition
#ifndef STRING1_H_
#define STRING1_H_
#include <iostream>
using std::ostream;
using std::istream;

class String
{
private:
    char * str;                            // pointer ot string
    int len;                            // length of string
    static int num_strings;                // number of objects
    static const int CINLIM = 80;        // cin input limit
public:
    // construction and other methods
    String(const char * s);             // constructor
    String();                            // default constructor
    String(const String &);                // copy constructor
    ~String();                            // destructor 
    int length() const { return len; }
    // overloaded operator methods
    String & operator=(const String &);
    String & operator=(const char *);
    char & operator[](int i);
    const char & operator[](int i)const;
    // overloaded operator friends
    friend bool operator<(const String &st, const String &st2);
    friend bool operator>(const String &st1, const String &st2);
    friend bool operator==(const String &st, const String &st2);
    friend ostream & operator<<(ostream & os, const String & st);
    friend istream & operator>>(istream & is, String & st);
    //static function
    static int HowMany();
};
#endif

类方法的实现。

// string1.cpp -- String class methods
#include <cstring>                    // string.h for some
#include "string1.h"                // includes <iostream>
using std::cin;
using std::cout;

// initializing static class member
int String::num_strings = 0;

// static method
int String::HowMany()
{
    return num_strings;
}

// class methods
String::String(const char * s)        // construct String from C string
{
    len = std::strlen(s);             // set size
    str = new char[len + 1];        // allot storage
    std::strcpy(str, s);            // initialize pointer
    num_strings++;                     // set object count
}

String::String()                    // default constructor
{
    len = 4;
    str = new char[1];
    str[0] = '';                    // default string
    num_strings++;
}

String::String(const String & st)
{
    num_strings++;                     // handle static member update
    len = st.len;                    // same length
    str = new char [len + 1];        // allot space 
    std::strcpy(str, st.str);        // copy string to new location
}

String::~String()                      // necesserary destructor
{
    --num_strings;                    // required
    delete [] str;                     // required
}

// overloaded operator methods

    // assign a String to a String
String & String::operator=(const String & st)
{
    if(this == &st)
        return *this;
    delete [] str;
    len = st.len;
    str = new char[len + 1];
    std::strcpy(str, st.str);
    return *this;
}

    // assign a C string to a String
String & String::operator=(const char * s)
{
    delete [] str;
    len = std::strlen(s);
    str = new char[len + 1];
    std::strcpy(str, s);
    return *this;
}

    // read-write char access for non-const String
char & String::operator[](int i)
{
    return str[i];
}

    // read-only char access for const string
const char & String::operator[](int i) const
{
    return str[i];
}

// averloaded operator friends

bool operator<(const String &st1, const String &st2)
{
    return (std::strcmp(st1.str, st2.str) < 0);
}

bool operator>(const String &st1, const String &st2)
{
    return st2 < st1;
}

bool operator==(const String &st1, const String &st2)
{
    return (std::strcmp(st1.str, st2.str)==0);
}

    // simple String output
ostream & operator<<(ostream & os, const String & st)
{
    os << st.str;
    return os;
}

    // quick and dirty String input
istream & operator>>(istream & is, String & st)
{
    char temp[String::CINLIM];
    is.get(temp, String::CINLIM);
    if(is)
        st = temp;
    while (is && is.get() != '
')
        continue;
    return is;
}

main（）， 测试String类。

// saying1.cpp -- using expanded String class 
// complile with string1.cpp
#include <iostream>
#include "string1.h"
const int MaxLen = 81;
int main()
{
    using std::cout;
    using std::cin;
    using std::endl;
    String name;
    cout << "Hi, what's your name?
>> ";
    cin >> name;

    cout << name << ", please enter up to " << ArSize
            << " short sayings <empty line to quit>:
";
    String sayings[ArSize];         // array of objects
    char temp[MaxLen]                // temporary string storage
    int i;
    for (i = 0; i < ArSize; i++)
    {
        cout << i + 1 << ": ";
        cin.get(temp, MaxLen);
        while(cin && cin.get()!='
')
            continue;
        if(!cin||temp[0] == '')    // empty line?
            break;                    // i not increamented
        else
            sayings[i] = temp;        // overloaded assignment
    }
    int total = i;                     // total # of lines read

    if( total > 0)
    {
        cout << "Here are your sayings:
";
        for (i = 0; i < total; i++)
            cout << sayings[i][0] << ": " << sayings[i] << endl;

        int shortest = 0;
        int first = 0;
        for(i = 1; i < total; i++)
        {
            if(sayings[i].length() < sayings[shortest].length())
                shortest = i;
            if(sayings[i] < sayings[first])
                first = i;
        }
        cout << "Shortest saying:
" << sayings[shortest] << endl;
        cout << "First alphabetically:
" << sayings[first] << endl;
        cout << "This program used " << String::HowMany()
                << " String objects. Bye.
"
    }
    else
        cout << "No input! Bye.
";
    return 0;
}

代码源自： C++ Primer Plus  。 小恪亲自敲写！

感悟：  如果一部书经久不衰， 一定是有它的理由的！ 正如这部书，  内容细致而深刻， 全面而严谨。获益良多！此书有点儿厚，与诸君共勉。