酒鬼隨機漫步（一個矢量類）

摘要:

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這是一個定義的一個矢量類，然后用矢量類模擬一個酒鬼的隨機漫步

問題很簡單，實現也不麻煩，但是這個小程序卻可以呈現出許多語法知識。而且代碼風格也不錯，因此保存在了這篇博客中。

建議：

?? ????1. 類的聲明以及函數的聲明放到一個文件夾內，?并且在一些必要的地方加上注釋！

　　?2.?函數的實現放到另一個文件內。

?????? 3.?將程序要具體解決的問題放到另外的一個文件里。（詳見代碼！）

好處：?把類的接口和實現細節分離開，?易于更改某個函數的功能。

??????????把函數的聲明和定義分開，?提高代碼可讀性。

??????????把類的聲明和定義?與?要解決的問題分開，?提高，類的重用性！

?????????????????????????????????????????定義類（聲明類內的函數）

// 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 modesprivate:double x;        // horizontal valuedouble y;        // vertical valuedouble mag;      // length of vector in degreesdouble ang;// direction of vector in degreesMode mode;  // private methods for setting valuesvoid 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 valuedouble yval() const {return y; }        // report y valuedouble magval() const {return mag; }    // report magnitudedouble angval() const {return ang; }    // report anglevoid polar_mode();                      // set mode to POLvoid rect_mode();                       // set mode to RECT// operator overloadingVector operator+(const Vector & b) const;Vector operator-(const Vector & b) const;Vector operator-()const;Vector operator*(double n) const;// friendsfriend Vector operator*(double n, const Vector & a);friend std::ostream & operator<<(std::ostream & os, const Vector & v);};
}    // end namespace VECTOR
#endif

?上面代碼涵蓋了許多關于類的基礎知識:??名稱空間與作用域?， ?實現類內部常量的方法， ?構造函數，?析構函數，?運算符重載，?友元函數,?關于多種實現方法等。

PS：?實現類內部常量的方法：?（1）枚舉類型。?（2）?static?const?int??常量

????????運算符重載：?注意操作數的順序。

???????????????????????????????????????????

?????????????????????????????????????????????????????????? 函數定義

// 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 radianconst double Rad_to_deg = 45.0/atan(1.0);// should be about 57.2957795130823// private methods// calculate magnitude from x and yvoid 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 coordinatevoid Vector::set_x(){x = mag*cos(ang);}//set y from polar coodinatevoid Vector::set_y(){y = mag * sin(ang);}// public methodsVector::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 pVector::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 POLvoid 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\n";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 VectorsVector 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 VectorVector Vector::operator-() const{return Vector(-x, -y);}// multiply vector by nVector Vector::operator*(double n) const{return Vector(n*x, n*y);}// friend methods// multiply n by Vector aVector operator*(double n, const Vector & a){return a * n;}//display rectangular coordinates if mode is RECT// else display polar coordinates if mode is POLstd::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 << ")"; }elseos << "Vector object mode is invalid";return os;}
}  // end namespace VECTOR

???????????????????????????????????????????????????????????具體解決的問題

// 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 generatordouble 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;return 0;
}

二。一個簡易的string類。

鍛煉內容：

??????????? 拷貝構造函數（深拷貝與淺拷貝）

??????????? 重載賦值運算符（深賦值）

??????????? 許多的細節與技巧！

類的聲明

//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 stringint len;                            // length of stringstatic int num_strings;                // number of objectsstatic const int CINLIM = 80;        // cin input limit
public:// construction and other methodsString(const char * s);             // constructorString();                            // default constructorString(const String &);                // copy constructor~String();                            // destructor int length() const { return len; }// overloaded operator methodsString & operator=(const String &);String & operator=(const char *);char & operator[](int i);const char & operator[](int i)const;// overloaded operator friendsfriend 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 functionstatic int HowMany();
};
#endif

View Code

類方法的實現。

// 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 sizestr = new char[len + 1];        // allot storagestd::strcpy(str, s);            // initialize pointernum_strings++;                     // set object count
}String::String()                    // default constructor
{len = 4;str = new char[1];str[0] = '\0';                    // default stringnum_strings++;
}String::String(const String & st)
{num_strings++;                     // handle static member updatelen = st.len;                    // same lengthstr = new char [len + 1];        // allot space std::strcpy(str, st.str);        // copy string to new location
}String::~String()                      // necesserary destructor
{--num_strings;                    // requireddelete [] 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 friendsbool 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() != '\n')continue;return is;
}

View Code

main（），測試String類。

// 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?\n>> ";cin >> name;cout << name << ", please enter up to " << ArSize<< " short sayings <empty line to quit>:\n";String sayings[ArSize];         // array of objectschar temp[MaxLen]                // temporary string storageint i;for (i = 0; i < ArSize; i++){cout << i + 1 << ": ";cin.get(temp, MaxLen);while(cin && cin.get()!='\n')continue;if(!cin||temp[0] == '\0')    // empty line?break;                    // i not increamentedelsesayings[i] = temp;        // overloaded assignment
    }int total = i;                     // total # of lines readif( total > 0){cout << "Here are your sayings:\n";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:\n" << sayings[shortest] << endl;cout << "First alphabetically:\n" << sayings[first] << endl;cout << "This program used " << String::HowMany()<< " String objects. Bye.\n"}elsecout << "No input! Bye.\n";return 0;
}