C++Primer Plus笔记——第十五章 友元、异常和其他课后编程练习答案

课后编程练习答案

习题1                习题2               习题3             习题4

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习题1

//tv.h
#ifndef TV_H_
#define TV_H_
#include 

using namespace std;

class Tv
{
	friend class Remote;
public:
	enum { Off, On };
	enum { MinVal, MaxVal = 20 };
	enum { Antenna, Cable };
	enum { TV, DVD };
	enum { USUAL, EXCHANGE };
	Tv(int s = Off, int mc = 125) :state(s), volume(5), maxchannel(mc), channel(2), mode(Cable), input(TV) {}
	~Tv() {}
	void onoff() { state = (state == On) ? Off : On; }
	bool ison()const { return state == On; }
	bool volup();
	bool voldown();
	void chanup();
	void chandown();
	void set_mode() { mode = (mode == Antenna) ? Cable : Antenna; }
	void set_input() { input = (input == TV) ? DVD : TV; }
	void settings() const;
	void set_rmode(Remote &r);
private:
	int state;
	int volume;
	int maxchannel;
	int channel;
	int mode;
	int input;
};

class Remote
{
private:
	friend class Tv;
	enum { USUAL, EXCHANGE };
	int mode;
	int fmode;
public:
	Remote(int m = Tv::TV, int f = USUAL) :mode(m), fmode(f) {}
	bool volup(Tv&t) { return t.volup(); }
	bool voldown(Tv&t) { return t.voldown(); }
	void onoff(Tv&t) { t.onoff(); }
	void chanup(Tv&t) { t.chanup(); }
	void chandown(Tv&t) { t.chandown(); }
	void set_chan(Tv&t, int c) { t.channel = c; }
	void set_mode(Tv&t) { t.set_mode(); }
	void set_input(Tv&t) { t.set_input(); }
	void mode_show()const { cout << "Remote pretent mode is " << fmode << endl; }
};

inline void Tv::set_rmode(Remote &r)
{
	if (ison())
	{
		r.fmode = Remote::EXCHANGE;
		r.mode_show();
	}
}
#endif

//tvfm.h
#ifndef TVFM_H_
#define TVFM_H_
#include 
using namespace std;
class Tv;
class Remote
{
public:
	enum State { Off, On };
	enum { MinVal, MaxVal = 20 };
	enum { Antenna, Cable };
	enum { TV, DVD };
private:
	int mode;
public:
	Remote(int m = TV) :mode(m) {}
	bool volup(Tv&t);
	bool voldown(Tv&t);
	void onoff(Tv&t);
	void chanup(Tv&t);
	void chandown(Tv&t);
	void set_chan(Tv&t, int c);
	void set_mode(Tv&t);
	void set_input(Tv&t);
};
class Tv
{
public:
	friend void Remote::set_chan(Tv&t, int c);
	enum State { Off, On };
	enum { MinVal, MaxVal = 20 };
	enum { Antenna, Cable };
	enum { TV, DVD };
	Tv(int s = Off, int mc = 125) :state(s), volume(5),
		maxchannel(mc), channel(2), mode(Cable), input(TV) {}
	~Tv() {}
	void onoff() { state = (state == On) ? Off : On; }
	bool ison()const { return state == On; }
	bool volup();
	bool voldown();
	void chanup();
	void chandown();
	void set_mode() { mode = (mode == Antenna) ? Cable : Antenna; }
	void set_input() { input = (input == TV) ? DVD : TV; }
	void settings()const;
private:
	int state;
	int volume;
	int maxchannel;
	int channel;
	int mode;
	int input;
};
inline bool Remote::volup(Tv&t) { return t.volup(); }
inline bool Remote::voldown(Tv&t) { return t.voldown(); }
inline void Remote::onoff(Tv&t) { t.onoff(); }
inline void Remote::chanup(Tv&t) { t.chanup(); }
inline void Remote::chandown(Tv&t) { t.chandown(); }
inline void Remote::set_chan(Tv&t, int c) { t.channel = c; }
inline void Remote::set_mode(Tv&t) { t.set_mode(); }
inline void Remote::set_input(Tv&t) { t.set_input(); }
#endif

//tv.cpp
#include "tv.h"
//#include "tvfm.h"
bool Tv::volup()
{
	if (volume < MaxVal)
	{
		volume++;
		return true;
	}
	else
		return false;
}
bool Tv::voldown()
{
	if (volume > MinVal)
	{
		volume--;
		return true;
	}
	else
		return false;
} 
void Tv::chanup()
{
	if (channel < maxchannel)
		channel++;
	else
		channel = 1;
}
void Tv::chandown()
{
	if (channel > 1)
		channel--;
	else
		channel = maxchannel;
}
void Tv::settings()const
{
	cout << "TV is " << (state == Off ? "Off" : "On") << endl;
	if (state == On)
	{
		cout << "Volume setting = " << volume << endl;
		cout << "Channel setting = " << channel << endl;
		cout << "Mode = " << (mode == Antenna ? "antenna" : "cable") << endl;
		cout << "Input = " << (input == TV ? "TV" : "DVD") << endl;
	}
}

 

//use_tv.cpp
#include "tv.h"
int main()
{
	Tv s42;
	Remote grey;
	grey.mode_show();
	cout << "Initial settings for 42\" TV:\n";
	s42.settings();
	s42.onoff();
	s42.chanup();
	cout << "\nAdjusted settings for 42\" TV:\n";
	s42.settings();
	s42.set_rmode(grey);
	grey.set_chan(s42, 10);
	grey.volup(s42);
	grey.volup(s42);
	cout << "\n42\" settings after using remote:\n";
	s42.settings();
	Tv s58(Tv::On);
	s58.set_mode();
	grey.set_chan(s58, 28);
	cout << "\n58\" settings:\n";
	s58.settings();
	s58.set_rmode(grey);
	system("pause");
	return 0;
}

习题2

//exc_mean.h
#ifndef EXC_MEAN_H_
#define EXC_MEAN_H_
#include 
#include 
#include 
#include 
using namespace std;

class bad_hmean :public logic_error
{
private:
	string name;
public:
	explicit bad_hmean(const string &n = "hmean", const string &s = "Error in hmean()\n");
	string mesg();
	virtual ~bad_hmean() throw() {}
};

bad_hmean::bad_hmean(const string &n, const string &s) :name(n), logic_error(s) { }

inline string bad_hmean::mesg()
{
	return "hmean() arguments a=-b should be div a+b=0!\n";
}

class bad_gmean :public logic_error
{
private:
	string name;
public:
	explicitbad_gmean(const string &n = "gmean", const string &s = "Error in gmean()\n");
	stringmesg();
	virtual ~bad_gmean()throw() {}
};
bad_gmean::bad_gmean(const string &n, const string &s) :name(n), logic_error(s) { }

inline string bad_gmean::mesg()
{
	return "gmean() arguments should be >= 0\n";
}
#endif

//error.cpp
#include "exc_mean.h"
double hmean(double a, double b);
double gmean(double a, double b);
int main()
{
	double x, y, z;
	cout << "Enter two numbers:";
	while (cin >> x >> y)
	{
		try {
			z = hmean(x, y);
			cout << "Harmonic mean of " << x << " and " << y
				<< " is " << z << endl;
			cout << "Geomettric mean of " << x << " and " << y
				<< " is " << gmean(x, y) << endl;
			cout << "Enter next set of numbers : ";
		}
		catch (bad_hmean&bg)
		{
			cout << bg.what();
			cout << "Error message: \n" << bg.mesg() << endl;
			cout << "Try again.\n";
			continue;
		}
		catch (bad_gmean&hg)
		{
			cout << hg.what();
			cout << "Error message: \n" << hg.mesg() << endl;
			cout << "Sorry, you don't get to play and more.\n";
			break;
		}
	}
	cout << "Bye!\n";
	system("pause");
	return 0;
}
double hmean(double a, double b)
{
	if (a == -b)
		throw bad_hmean();
	return 2.0*a*b / (a + b);
}
double gmean(double a, double b)
{
	if (a < 0 || b < 0)
		throw bad_gmean();
	return sqrt(a*b);
}

习题3

#ifndef EXC_MEAN_H_
#define EXC_MEAN_H_
#include 
#include 
#include 
#include 
using namespace std;
class bad_hmean :public logic_error
{
private:
	string name;
public:
	double v1;
	double v2;
	explicitbad_hmean(double a = 0, double b = 0,
		const string &s = "Error in hmean()\n");
	voidmesg();
	virtual ~bad_hmean()throw() {}
};

bad_hmean::bad_hmean(double a, double b, const string &s):v1(a), v2(b), logic_error(s)
{
	name = "hmean";
}
inline void bad_hmean::mesg()
{
	cout << name << "(" << v1 << ", " << v2 << ") arguments a=-b should be div a+b=0!\n";
}
class bad_gmean :public bad_hmean
{
private:
	string name;
public:
	explicitbad_gmean(double a = 0, double b = 0,
		const string &s = "Error in gmean()\n");
	voidmesg();
	virtual ~bad_gmean()throw() {}
};

bad_gmean::bad_gmean(double a, double b, const string &s):bad_hmean(a, b, s)
{
	name = "gmean";
}

inline void bad_gmean::mesg()
{
	cout << name << "(" << bad_hmean::v1 << ", " << bad_hmean::v2 << ") arguments should be >= 0\n";
}
#endif

//error.cpp
#include "exc_mean.h"
double hmean(double a, double b);
double gmean(double a, double b);
int main()
{
	double x, y, z;
	cout << "Enter two numbers:";
	while (cin >> x >> y)
	{
		try {
			z = hmean(x, y);
			cout << "Harmonic mean of " << x << " and " << y
				<< " is " << z << endl;
			cout << "Geomettric mean of " << x << " and " << y
				<< " is " << gmean(x, y) << endl;
			cout << "Enter next set of numbers : ";
		}
		catch (bad_gmean&hg)
		{
			cout << hg.what();
			cout << "Error message: \n";
			hg.mesg();
			cout << endl;
			cout << "Sorry, you don't get to play and more.\n";
			break;
		}
		catch (bad_hmean&bg)
		{
			cout << bg.what();
			cout << "Error message: \n";
			bg.mesg();
			cout << endl;
			cout << "Try again.\n";
			continue;
		}
	}
	cout << "Bye!\n";
	system("pause");
	return 0;
}
doublehmean(double a, double b)
{
	if (a == -b)
		throw bad_hmean();
	return 2.0*a*b / (a + b);
}
doublegmean(double a, double b)
{
	if (a < 0 || b < 0)
		throw bad_gmean();
	return sqrt(a*b);
}

习题4

//sales.h
#ifndef SALES_H_
#define SALES_H_
#include 
#include 
#include 
#include 
#include 
using namespace std;

class Sales
{
public:
	enum { MONTHS = 12 };
	class bad_index :public logic_error
	{
	private:
		int bi;
	public:
		explicit bad_index(int ix, const string &s = "Index error in Sales object\n");
		int bi_val()const { return bi; }
		virtual ~bad_index()throw() {}
	};
	explicit Sales(int yy = 0);
	Sales(int yy, const double *gr, int n);
	virtual ~Sales() {}
	int Year()const { return year; }
	virtual double operator[](int i)const;
	virtual double &operator[](int i);
private:
	double gross[MONTHS];
	int year;
};
class LabeledSales :public Sales
{
public:
	class nbad_index : public Sales::bad_index
	{
	private:
		std::string lbl;
	public:
		nbad_index(const string &lb, int ix,
			const string &s = "Index error in LabeledSales object\n");
		const string &label_val()const { return lbl; }
		virtual ~nbad_index()throw() {}
	};
	explicit LabeledSales(const string &lb = "none", int yy = 0);
	LabeledSales(const string &lb, int yy, const double *gr, int n);
	virtual ~LabeledSales() {}
	const string &Label()const { return label; }
	virtual double operator[](int i)const;
	virtual double &operator[](int i);
private:
	string label;
};
#endif

//sales.cpp
#include "sales.h"
Sales::bad_index::bad_index(int ix,
  const string &s) :logic_error(s), bi(ix)
{
}
Sales::Sales(int yy)
{
  year = yy;
  for (int i = 0; i < MONTHS; ++i)
	  gross[i] = 0;
}
Sales::Sales(int yy, const double *gr, int n)
{
  year = yy;
  int lim = (n < MONTHS) ? n : MONTHS;
  int i;
  for (i = 0; i < lim; ++i)
	  gross[i] = gr[i];
  for (; i < MONTHS; ++i)
	  gross[i] = 0;
}
double Sales::operator[](int i)const
{
  if (i < 0 || i >= MONTHS)
	  throw bad_index(i);
  return gross[i];
}
double&Sales::operator[](int i)
{
  if (i < 0 || i >= MONTHS)
	  throw bad_index(i);
  return gross[i];
}
LabeledSales::nbad_index::nbad_index(const string &lb, int ix,
  const string &s) :Sales::bad_index(ix, s)
{
  lbl = lb;
}
LabeledSales::LabeledSales(const string &lb, int yy) : Sales(yy)
{
  label = lb;
}
LabeledSales::LabeledSales(const string &lb, int yy, const double *gr, int n) : Sales(yy, gr, n)
{
  label = lb;
}
double LabeledSales::operator[](int i)const
{
  if (i < 0 || i >= MONTHS)
	  throw nbad_index(Label(), i);
  return Sales::operator[](i);
}
double&LabeledSales::operator[](int i)
{
  if (i < 0 || i >= MONTHS)
	  throw nbad_index(Label(), i);
  return Sales::operator[](i);
}

//use_sales.cpp
#include "sales.h"
int main()
{
	double vals1[12] =
	{
	1220, 1100, 1122, 2212, 1232, 2334,
	2884, 2393, 3302, 2922, 3002, 3544
	};
	double vals2[12] =
	{
	12, 11, 22, 21, 32, 24,
	28, 29, 33, 29, 32, 35
	};
	Sales sales1(2011, vals1, 12);
	LabeledSales sales2("Blogstar", 2012, vals2, 12);
	Sales::bad_index *s;
	LabeledSales::nbad_index *l;
	cout << "First try block:\n";
	try
	{
		int i;
		cout << "Year = " << sales1.Year() << endl;
		for (i = 0; i < 12; ++i)
		{
			cout << sales1[i] << ' ';
			if (i % 6 == 5)
				cout << endl;
		}
		cout << "Year = " << sales2.Year() << endl;
		cout << "Label = " << sales2.Label() << endl;
		for (i = 0; i <= 12; ++i)
		{
			cout << sales2[i] << ' ';
			if (i % 6 == 5)
				cout << endl;
		}
		cout << "End of try block 1.\n";
	}
	catch (logic_error&bad)
	{
		cout << bad.what();
		if (l = dynamic_cast(&bad))
		{
			cout << "Comany: " << l->label_val() << endl;
			cout << "bad index: " << l->bi_val() << endl;
		}
		else if (s = dynamic_cast(&bad))
			cout << "bad index: " << s->bi_val() << endl;
	}
	cout << "\nNext try block:\n";
	try
	{
		sales2[2] = 37.5;
		sales1[20] = 23345;
		cout << "End of try block 2.\n";
	}
	catch (logic_error&bad)
	{
		cout << bad.what();
		if (l = dynamic_cast(&bad))
		{
			cout << "Comany: " << l->label_val() << endl;
			cout << "bad index: " << l->bi_val() << endl;
		}
		else if (s = dynamic_cast(&bad))
			cout << "bad index: " << s->bi_val() << endl;
	}
	cout << "done\n";
	system("pause");
	return 0;
}