C++ primer习题记录——第七章

7.1：

#include 
using namespace std;
 
struct Sales_data
{
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
};
int main()
{
	Sales_data total;
	if (cin >> total.bookNo >> total.unit_sold >> total.revenue)
	{
		Sales_data trans;
		while (cin >> trans.bookNo >> trans.unit_sold >> trans.revenue)
		{
			if (total.bookNo == trans.bookNo)
			{
				total.unit_sold += trans.unit_sold;
				total.revenue += trans.revenue;
			}
			else
			{
				cout << total.bookNo << " " << total.unit_sold << " " << total.revenue << endl;
				total.bookNo = trans.bookNo;
				total.unit_sold = trans.unit_sold;
				total.revenue = trans.revenue;
			}
		}
		cout << total.bookNo << " " << total.unit_sold << " " << total.revenue << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

   7.3：

#include 
using namespace std;
 
struct Sales_data
{
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
int main()
{
	Sales_data total;
	if (cin >> total.bookNo >> total.unit_sold >> total.revenue)
	{
		Sales_data trans;
		while (cin >> trans.bookNo >> trans.unit_sold >> trans.revenue)
		{
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				cout << total.bookNo << " " << total.unit_sold << " " << total.revenue << endl;
				total.bookNo = trans.bookNo;
				total.unit_sold = trans.unit_sold;
				total.revenue = trans.revenue;
			}
		}
		cout << total.bookNo << " " << total.unit_sold << " " << total.revenue << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

  7.5：

#include 
using namespace std;
struct Person
{
	string Show_add()const
	{
		return this->m_address;
	}
	string Show_name()const
	{
		return this->m_name;
	}
	string m_name;
	string m_address;
};

int main()
{
	Person p1;
	p1.m_name = "张三";
	p1.m_address = "花园";
	cout << p1.Show_name() << " " << p1.Show_add() << endl;
	system("pause");
	return 0;
}

7.7：

#include 
using namespace std;

struct Sales_data
{
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}
int main()
{
	Sales_data total;
	if (read(cin,total))
	{
		Sales_data trans;
		while (read(cin,trans))
		{
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				print(cout, total) << endl;
				total = trans;
			}
		}
		print(cout, total) << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

  7.9：

#include 
using namespace std;
class Person
{
public:
	string Show_add()const
	{
		return this->m_address;
	}
	string Show_name()const
	{
		return this->m_name;
	}
	string m_name;
	string m_address;
};
istream& read(istream& is, Person& p1)
{
	is >> p1.m_name >> p1.m_address;
	return is;
}
ostream& print(ostream& os, const Person& p1)
{
	os << "姓名： " << p1.Show_name() << " 住址： " << p1.Show_add() << endl;
	return os;
}
int main()
{
	Person p1;
	if (read(cin, p1))
	{
		print(cout, p1);
	}
	
	system("pause");
	return 0;
}

  7.11:

#include 
using namespace std;

struct Sales_data
{
	Sales_data() = default;
	Sales_data(const string& s) :bookNo(s) {};
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p) {};
	Sales_data(istream& is);
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}
Sales_data::Sales_data(istream& is)
{
	read(is, *this);
}
int main()
{
	Sales_data s1;
	print(cout, s1) << endl;
	Sales_data s2("0-201-78345-x");
	print(cout, s2) << endl;
	Sales_data s3("0-201-78345-x", 3, 20.00);
	print(cout, s3) << endl;
	Sales_data s4(cin);
	print(cout, s4) << endl;
	system("pause");
	return 0;
}

7.12:

#include 
using namespace std;
struct Sales_data;//要在read函数之前声明不然read函数找不到sales_data类
istream& read(istream& is, Sales_data& item);//要在sales_data类之前声明read函数！！
struct Sales_data
{
	Sales_data() = default;
	Sales_data(const string& s) :bookNo(s) {};
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p) {};
	Sales_data(istream& is) { read(cin, *this); }
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}
//Sales_data::Sales_data(istream& is)
//{
//	read(is, *this);
//}
int main()
{
	Sales_data s1;
	print(cout, s1) << endl;
	Sales_data s2("0-201-78345-x");
	print(cout, s2) << endl;
	Sales_data s3("0-201-78345-x", 3, 20.00);
	print(cout, s3) << endl;
	Sales_data s4(cin);
	print(cout, s4) << endl;
	system("pause");
	return 0;
}

7.13:

#include 
using namespace std;
struct Sales_data;//要在read函数之前声明不然read函数找不到sales_data类
istream& read(istream& is, Sales_data& item);//要在sales_data类之前声明read函数！！
struct Sales_data
{
	Sales_data() = default;
	Sales_data(const string& s) :bookNo(s) {};
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p) {};
	Sales_data(istream& is) { read(cin, *this); }
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}

int main()
{
	Sales_data total(cin);
	if (!total.isbn().empty())
	{
		
		while (cin)
		{
			Sales_data trans(cin);
			if (!cin) { break; }
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				print(cout, total) << endl;
				total = trans;
			}
		}
		print(cout, total) << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

7.15:

#include 
using namespace std;
class Person;
istream& read(istream& is, Person& p1);
class Person
{
public:
	Person() = default;
	Person(string name, string address)
	{
		this->m_name = name;
		this->m_address = address;
	}
	Person(istream& is)
	{
		read(is, *this);
	}
	string Show_add()const
	{
		return this->m_address;
	}
	string Show_name()const
	{
		return this->m_name;
	}
	string m_name;
	string m_address;
};
istream& read(istream& is, Person& p1)
{
	is >> p1.m_name >> p1.m_address;
	return is;
}
ostream& print(ostream& os, const Person& p1)
{
	os << "姓名： " << p1.Show_name() << " 住址： " << p1.Show_add() << endl;
	return os;
}
int main()
{
	Person p1;
	if (read(cin, p1))
	{
		print(cout, p1);
	}
	Person p2("张三", "花园");
	print(cout, p2);
	Person p3(cin);
	print(cout, p3);

	system("pause");
	return 0;
}

7.21:

#include 
using namespace std;
struct Sales_data;//要在read函数之前声明不然read函数找不到sales_data类
istream& read(istream& is, Sales_data& item);//要在sales_data类之前声明read函数！！
class Sales_data
{
	friend istream& read(istream& is, Sales_data& item);
	friend ostream& print(ostream& os, const Sales_data& item);
	friend Sales_data add(const Sales_data& s1, const Sales_data& s2);
public:
	Sales_data() = default;
	Sales_data(const string& s) :bookNo(s) {};
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p) {};
	Sales_data(istream& is) { read(cin, *this); }
	
	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
private:
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}

int main()
{
	Sales_data total(cin);
	if (!total.isbn().empty())
	{

		while (cin)
		{
			Sales_data trans(cin);
			if (!cin) { break; }
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				print(cout, total) << endl;
				total = trans;
			}
		}
		print(cout, total) << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

7.22:

#include 
using namespace std;

class Person
{
	friend istream& read(istream& is, Person& p1);
	friend ostream& print(ostream& os, const Person& p1);
public:
	Person() = default;
	Person(string name, string address)
	{
		this->m_name = name;
		this->m_address = address;
	}
	Person(istream& is)
	{
		read(is, *this);
	}
	string Show_add()const
	{
		return this->m_address;
	}
	string Show_name()const
	{
		return this->m_name;
	}
private:
	string m_name;
	string m_address;
};
istream& read(istream& is, Person& p1)
{
	is >> p1.m_name >> p1.m_address;
	return is;
}
ostream& print(ostream& os, const Person& p1)
{
	os << "姓名： " << p1.Show_name() << " 住址： " << p1.Show_add() << endl;
	return os;
}
int main()
{
	Person p1;
	if (read(cin, p1))
	{
		print(cout, p1);
	}
	Person p2("张三", "花园");
	print(cout, p2);
	Person p3(cin);
	print(cout, p3);

	system("pause");
	return 0;
}

7.23:

#include 
using namespace std;
#include
class Screen
{
public:
	using pos = string::size_type;
	Screen() = default;
	Screen(pos ht, pos wd, char c)
	{
		this->height = ht;
		this->width = wd;
		this->contents.assign(ht * wd, c);
	}
	char get()const
	{
		return contents[cursor];
	}
	inline char get(pos r, pos c)const;
	Screen& move(pos r, pos c);
private:
	pos cursor = 0;
	pos height = 0, width = 0;
	string contents;
};
char Screen::get(pos r, pos c)const
{
	pos row = r * width;
	return contents[row + c];
}
inline Screen& Screen::move(pos r, pos c)
{
	pos row = r * width;
	cursor = row + c;
	return *this;
}
int main()
{

	system("pause");
	return 0;
}

7.24:

#include 
using namespace std;
#include
class Screen
{
public:
	using pos = string::size_type;
	Screen() = default;
	Screen(pos ht, pos wd, char c)
	{
		this->height = ht;
		this->width = wd;
		this->contents.assign(ht * wd, c);
	}
	Screen(pos ht, pos wd)
	{
		this->height = ht;
		this->width = wd;
		this->contents.assign(ht * wd, ' ');
	}
	char get()const
	{
		return contents[cursor];
	}
	inline char get(pos r, pos c)const;
	Screen& move(pos r, pos c);
private:
	pos cursor = 0;
	pos height = 0, width = 0;
	string contents;
};
char Screen::get(pos r, pos c)const
{
	pos row = r * width;
	return contents[row + c];
}
inline Screen& Screen::move(pos r, pos c)
{
	pos row = r * width;
	cursor = row + c;
	return *this;
}
int main()
{

	system("pause");
	return 0;
}

7.26:

#include 
using namespace std;

class Sales_data
{
	friend istream& read(istream& is, Sales_data& item);
	friend ostream& print(ostream& os, const Sales_data& item);
	friend Sales_data add(const Sales_data& s1, const Sales_data& s2);
public:
	Sales_data() = default;
	Sales_data(const string& s) :bookNo(s) {};
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p) {};
	Sales_data(istream& is) { read(cin, *this); }

	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
private:
	inline double avg_price()const;
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}
inline double Sales_data::avg_price()const
{
	return unit_sold ? revenue / unit_sold : 0;
}
int main()
{
	Sales_data total(cin);
	if (!total.isbn().empty())
	{

		while (cin)
		{
			Sales_data trans(cin);
			if (!cin) { break; }
			if (total.isbn() == trans.isbn())
			{
				total.combine(trans);
			}
			else
			{
				print(cout, total) << endl;
				total = trans;
			}
		}
		print(cout, total) << endl;
	}
	else
	{
		cout << " no data !" << endl;
	}
	system("pause");
	return 0;
}

7.27：      

#include 
using namespace std;
#include
class Screen
{
public:
	using pos = string::size_type;
	Screen() = default;
	Screen(pos ht, pos wd, char c):height(ht),width(wd),contents(ht*wd,c) {}
	Screen(pos ht, pos wd):height(ht), width(wd), contents(ht* wd, ' ') {}

	char get()const
	{
		return contents[cursor];
	}
	inline char get(pos r, pos c)const;
	inline Screen& move(pos r, pos c);
	inline Screen& set(char);
	inline Screen& set(pos r, pos c, char ch);
	Screen& display(ostream& os)
	{
		do_display(os);
		return *this;
	}
	const Screen& display(ostream& os)const
	{
		do_display(os);
		return *this;
	}
private:
	void do_display(ostream& os)const
	{
		os << contents;
	}
	pos cursor = 0;
	pos height = 0, width = 0;
	string contents;
};
char Screen::get(pos r, pos c)const
{
	pos row = r * width;
	return contents[row + c];
}
inline Screen& Screen::move(pos r, pos c)
{
	pos row = r * width;
	cursor = row + c;
	return *this;
}
inline Screen& Screen::set(char c)
{
	this->contents[cursor] = c;
	return *this;
}
inline Screen& Screen::set(pos r, pos c, char ch)
{
	this->contents[r * width + c] = ch;
	return *this;
}
int main()
{
	Screen myScreen(5, 5, 'x');
	myScreen.move(4, 0).set('#').display(cout);
	cout << endl;
	myScreen.display(cout);
	cout << endl;
	system("pause");
	return 0;
}

7.31:

class Y;
class X
{
	Y* py = 0;
};
class Y
{
	X x1;
};

 7.32:

#include 
using namespace std;
#include
#include
class Screen;
class Window_mgr
{
public:
	using ScreenIndex = vector::size_type;
	void clear(ScreenIndex);
private:
	vectorscreens;
};
class Screen
{
	friend void Window_mgr::clear(ScreenIndex);
public:
	using pos = string::size_type;
	Screen() = default;
	Screen(pos ht, pos wd, char c) :height(ht), width(wd), contents(ht* wd, c) {}
	Screen(pos ht, pos wd) :height(ht), width(wd), contents(ht* wd, ' ') {}

	char get()const
	{
		return contents[cursor];
	}
	inline char get(pos r, pos c)const;
	inline Screen& move(pos r, pos c);
	inline Screen& set(char);
	inline Screen& set(pos r, pos c, char ch);
	Screen& display(ostream& os)
	{
		do_display(os);
		return *this;
	}
	const Screen& display(ostream& os)const
	{
		do_display(os);
		return *this;
	}
private:
	void do_display(ostream& os)const
	{
		os << contents;
	}
	pos cursor = 0;
	pos height = 0, width = 0;
	string contents;
};
char Screen::get(pos r, pos c)const
{
	pos row = r * width;
	return contents[row + c];
}
inline Screen& Screen::move(pos r, pos c)
{
	pos row = r * width;
	cursor = row + c;
	return *this;
}
inline Screen& Screen::set(char c)
{
	this->contents[cursor] = c;
	return *this;
}
inline Screen& Screen::set(pos r, pos c, char ch)
{
	this->contents[r * width + c] = ch;
	return *this;
}

void Window_mgr::clear(ScreenIndex i)
{
	Screen& s = screens[i];
	s.contents = string(s.height * s.width, ' ');
}

7.41：

#include 
using namespace std;

class Sales_data
{
	friend istream& read(istream& is, Sales_data& item);
	friend ostream& print(ostream& os, const Sales_data& item);
	friend Sales_data add(const Sales_data& s1, const Sales_data& s2);
public:
	Sales_data(const string& s, unsigned n, double p) :bookNo(s), unit_sold(n), revenue(n* p)
	{
		cout << "这是三参数构造函数调用" << endl;
	};
	Sales_data() :Sales_data(" ", 0, 0) { cout << "这是默认函数调用" << endl; }
	Sales_data(string s):Sales_data(s,0,0){ cout << "这是string构造函数调用" << endl; }
	Sales_data(istream& is) :Sales_data() {
		cout << "这是isteam构造函数调用" << endl;
		read(is, *this); };

	Sales_data& combine(const Sales_data& rhs);
	string isbn()const
	{
		return this->bookNo;
	}
private:
	inline double avg_price()const;
	string bookNo;
	unsigned unit_sold = 0;
	double revenue = 0.0;
};
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
	this->unit_sold += rhs.unit_sold;
	this->revenue += rhs.revenue;
	return *this;
}
Sales_data add(const Sales_data& s1, const Sales_data& s2)
{
	Sales_data temp = s1;
	temp.combine(s2);
	return temp;
}
istream& read(istream& is, Sales_data& item)
{
	double price = 0;
	is >> item.bookNo >> item.unit_sold >> price;
	item.revenue = item.unit_sold * price;
	return is;
}
ostream& print(ostream& os, const Sales_data& item)
{
	os << item.bookNo << " " << item.unit_sold << " " << item.revenue;
	return os;
}
inline double Sales_data::avg_price()const
{
	return unit_sold ? revenue / unit_sold : 0;
}
int main()
{
	Sales_data s1("sad", 1, 1);
	Sales_data s2;
	Sales_data s3("bad");
	Sales_data s4(cin);
	system("pause");
	return 0;
}

7.43：

#include
using namespace std;

class NoDefault
{
public:
	NoDefault(int) { cout << "这是nodefault的构造函数" << endl; }
};
class C
{
public:
	C():c(0){ cout << "这是C的构造函数" << endl; }
	NoDefault c;
};
int main()
{
	C c;
	system("pause");
	return 0;
}

7.50：

#include 
using namespace std;

class Person
{
	friend istream& read(istream& is, Person& p1);
	friend ostream& print(ostream& os, const Person& p1);
public:
	Person() = default;
	Person(string name, string address)
	{
		this->m_name = name;
		this->m_address = address;
	}
	explicit Person(istream& is)
	{
		read(is, *this);
	}
	string Show_add()const
	{
		return this->m_address;
	}
	string Show_name()const
	{
		return this->m_name;
	}
private:
	string m_name;
	string m_address;
};
istream& read(istream& is, Person& p1)
{
	is >> p1.m_name >> p1.m_address;
	return is;
}
ostream& print(ostream& os, const Person& p1)
{
	os << "姓名： " << p1.Show_name() << " 住址： " << p1.Show_add() << endl;
	return os;
}
int main()
{
	Person p1;
	if (read(cin, p1))
	{
		print(cout, p1);
	}
	Person p2("张三", "花园");
	print(cout, p2);
	Person p3(cin);
	print(cout, p3);

	system("pause");
	return 0;
}

7.51：

找的别人的回答QAQ

//Such as a function like that:

int getSize(const std::vector&);
//if vector has not defined its single-argument constructor as explicit. we can use the function like:

getSize(34);
//What is this mean? It's very confused.

//But the std::string is different. In ordinary, we use std::string to replace const char *(the C language). so when we call a function like that:

void setYourName(std::string); // declaration.
setYourName("pezy"); // just fine.
//it is very natural.

 7.53:

class Debug
{
public:
	constexpr Debug(bool b =true):hw(b),io(b),other(b){}
	constexpr Debug(bool h,bool i, bool o): hw(h), io(i), other(o) {}
	constexpr bool any()
	{
		return hw || io || other;
	}
	void set_io(bool b) { io = b; }
	void set_hwo(bool b) { hw = b; }
	void set_other(bool b) { other = b; }
private:
	bool hw; //硬件错误
	bool io; //io错误
	bool other;
};

7.57:

class Account {
public:
    void calculate() { amount += amount * interestRate; }
    static double rate() { return interestRate; }
    static void rate(double newRate) { interestRate = newRate; }
    
private:
    std::string owner;
    double amount;
    static double interestRate;
    static constexpr double todayRate = 42.42;
    static double initRate() { return todayRate; }
};

double Account::interestRate = initRate();