C++ Primer Plus第六版编程练习11.1解答

vect.h

// 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
double ang; // direction of vector in degrees
Mode mode; // RECT or POL
// 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


vect.cpp
// vect.cpp -- methods for the Vector class
#include <cmath>
#include "vect.h" // includes <iostream>

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 methods
// 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 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\n";
x = y = mag = ang = 0.0;
mode = RECT;
}
}

// reset vector from rectangular coordinates if form is
// RECT (the default) or else from 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\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 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


randwalk.cpp
// randwalk.cpp -- using the Vector class
// compile with the vect.cpp file
#include <iostream>
#include <cstdlib> // rand(), srand(), exit() prototypes
#include <ctime> // time() prototype
#include "vect.h"
#include <fstream> //for file I/O

int main()
{
using namespace std;
using VECTOR::Vector;

ofstream fout;
fout.open("randwalkResult.txt");
if(!fout.is_open())
{
cout<<"Could not open the file.\nProgam terminating.\n";
exit(EXIT_FAILURE);
}

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;
fout << "Target distance: "<<target<<" , Step Size: "<<dstep<<endl;

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

//write this result to the file
fout << "After " << steps << " steps, the subject "
"has the following location:\n";
result.rect_mode();
fout << result << endl;
result.polar_mode();
fout << " or\n" << result << endl;
fout << "Average outward distance per step = "
<< result.magval()/steps << endl<<endl;

steps = 0;
result.reset(0.0, 0.0);
cout << "\nEnter target distance (q to quit): ";
}
cout << "\nBye!\n";

fout.close();
cin.get();
return 0;
}