標頭檔案
#ifndef VECTOR_H_//避免標頭檔案的重定義，如果XX沒有被定義
#define VECTOR_H_//就定義XX，刪除可使#ifndef與#endif之間的程式碼不執行

#include<iostream>

namespace VECTOR//用來區分名字相同的變數和函式
{
	class Vector
	{
	public:
		enum Mode{RECT,POL};//Mode列舉名，RECT=0，POL=1
	private:
		double x;
		double y;
		double mag;
		double ang;
		Mode mode;
		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;}
		double yval() const {return y;}
		double magval() const {return mag;}
		double angval() const {return ang;}
		void polar_mode();
		void rect_mode();

		Vector operator+(const Vector &b)const;
		Vector operator-(const Vector &b)const;
		Vector operator-()const;
		Vector operator*(double n)const;

		friend Vector operator*(double n,const Vector &a);
		friend std::ostream &operator<<(std::ostream &os,const Vector & v);
	};
}





#endif
 

#include<cmath>
#include "vector.h"

using namespace std;

namespace VECTOR
{
	const double Rad_to_deg=45.0/atan(1.0);//atan(1)=45度，求1弧度等於多少度
	void Vector::set_mag()
	{
		mag=sqrt(x*x+y*y);
	}

	void Vector::set_ang()
	{
		if(0==x&&y==0)
			ang=0;
		else
			ang=atan2(y,x);
	}

	void Vector::set_x()
	{
		x=mag*sin(ang);
	}

	void Vector::set_y()
	{
		y=mag*cos(ang);
	}

	Vector::Vector()
	{
		x=y=mag=ang=0;
	}

	Vector::Vector(double n1,double n2,Mode form)
	{
		mode=form;
		if(mode==RECT)
		{
			x=n1;
			y=n2;
			set_mag();
			set_ang();
		}
		else if(mode==POL)
		{
			mag=n1;
			ang=n2/Rad_to_deg;
			set_x();
			set_y();
		}
		else
		{
			cout<<"Incorrect 3rd arguement to Vector() --";
			cout<<"vector set to 0\n";
			x=y=mag=ang=0;
			mode=RECT;
		}
	}

	void Vector::reset(double n1,double n2,Mode form)
	{
		mode=form;
		if(mode==RECT)
		{
			x=n1;
			y=n2;
			set_mag();
			set_ang();
		}
		else if(mode==POL)
		{
			mag=n1;
			ang=n2/Rad_to_deg;
			set_x();
			set_y();
		}
		else
		{
			cout<<"Incorrect 3rd arguement to Vector() --";
			cout<<"vector set to 0\n";
			x=y=mag=ang=0;
			mode=RECT;
		}
	}

	Vector::~Vector(){}

	void Vector::polar_mode()
	{
		mode=POL;
	}

	void Vector::rect_mode()
	{
		mode=RECT;
	}

	Vector Vector::operator+(const Vector &b)const
	{
		return Vector(x+b.x,y+b.y);
	}

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

	Vector Vector::operator-()const
	{
		return Vector(-x,-y);
	}

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

	Vector operator*(double n,const Vector &a)
	{
		return a*n;
	}

	ostream &operator<<(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;
	}



}
 

#include<iostream>
#include<cstdlib>
#include<ctime>
#include "vector.h"
#include<fstream>
#include<windows.h>

using namespace std;


void main()
{
	using VECTOR::Vector;
	srand(time(0));
	double direction;
	Vector step;
	Vector result(0,0);
	unsigned long steps=0;
	double target;
	double dstep;
	ofstream outfile;
	outfile.open("1.txt");
	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;

		outfile<<steps<<": "<<result<<endl;
		while(result.magval()<target)
		{
			direction=rand()%360;
			step.reset(dstep,direction,Vector::POL);
			result=result+step;

			steps++;
			outfile<<steps<<": "<<result<<endl;
		}
		outfile<<"After "<<steps<<" steps,the subject has the following location:\n";
		outfile<<result<<endl;
		result.polar_mode();
		outfile<<" or\n"<<result<<endl;
		outfile<<"Average outward distance per step="<<result.magval()/steps<<endl;
		steps=0;
		result.reset(0,0);
		cout<<"Enter target distance (q to quit):";
	}

	cout<<"Bye!\n";
	WinExec( "notepad.exe 1.txt", SW_SHOW );//在c++程式碼中開啟檔案

	cin.clear();
	while(cin.get()!='\n')
		continue;
}