Question

关于c++图书类型求解

定义一个Book（图书）类，在该类定义中包括数据成员： m_Bookname（书名）；m_Number（存书数量）；m_Price（价格）和m_Count（静态数据成员，统计图书对象的个数）。成员函数：带默认参数构造函数，复制构造函数，析构函数，Display()显示图书的情况；Borrow()将存书数量减1，并显示当前存书数量；Restore()将存书数量加1，并显示当前存书数量。使用一个友元函数来计算书本的总价（m_Number* m_Price）。编写main函数来调用测试。
我的函数：
#include <iostream>
using namespace std;
class Book{
public:
Book(char mBookname,int mNumber,double mPrice,double mCount);
void Display();
void Borrow();
void Restore();
friend double sum(Book &mNumber,Book &mPrice);
private:
char bookname;
double price;
int number;
};
Book::Book(char mBookname,int mNumber,double mPrice){
bookname=mBookname;
number=mNumber;
price=mPrice;
}
void Book::Display(){
cout<<"The bookname is "<<bookname<<" and its price is "<<price<<", we have
"<<number<<"of them."<<endl;
}
void Book::Borrow(){
number=number-1;
cout<<"We have"<<number<<"books left."<<endl;
}
void Book::Restore(){
number=number+1;
cout<<"We have "<<number<<"books left."<<endl;
}
int main()
{
Book book("C++ primer", 99.00, 6);
int choice;
cout << "1-->display the information of the book" << endl;
cout << "2-->borrow book" << endl;
cout << "3-->restore book" << endl;
int contin = 1;
while(contin)
{
cout << "Please input the function you want: ";
cin >> choice;
switch(choice)
{
case 1:book.Display();break;
case 2:book.Borrow();break;
case 3:book.Restore();break;
default:cout << "wrong operation!";break;
}
cout <<"continue? 1-->yes or 0-->no: ";
cin >> contin;
}
return 0;
}
错哪里了，友元函数怎么加入？？？

Answer 1

#include <iostream>
using namespace std;
#define MAXSIZE  10
class Book
{
public:
	//Book(char mBookname, int mNumber, double mPrice, double mCount);
	//书名应该为字符串，不应该是字符。可以用字符数组，也可以用string类
	Book(char* mBookname, int mNumber, double mPrice);
	~Book();		//析构函数

public:
	void Display();
	void Borrow();
	void Restore();
	//friend double sum(Book &mNumber, Book &mPrice);
	friend double sum(Book& book);
private:
	//char bookname;
	char bookname[MAXSIZE];
	double price;
	int number;

	static int m_Count;		//静态字段
};

int Book::m_Count = 0;			//静态数据成员在类外初始化

//Book::Book(char mBookname, int mNumber, double mPrice)
Book::Book(char* mBookname, int mNumber, double mPrice)
{
	//bookname = mBookname;
	strcpy(bookname, mBookname);
	number = mNumber;
	price = mPrice;
	m_Count++;			//每构造一个Book对象，计数+1
}

Book::~Book()
{
	m_Count--;			//每析构一个Book对象，计数-1
}

void Book::Display(){
	/*cout << "The bookname is " << bookname << " and its price is " << price << ", we have
		"<<number<<"of them."<<endl;*/
	cout << "The bookname is " << bookname << " and its price is " << price << ", we have"\
		<<number<<"of them."<<endl;
	//若要换行，要在行尾加 \ 
}
void Book::Borrow(){
	number = number - 1;
	cout << "We have" << number << "books left." << endl;
}
void Book::Restore(){
	number = number + 1;
	cout << "We have " << number << "books left." << endl;
}

double sum(Book& book)
{
	return book.number*book.price;
}

int main()
{
	//Book book("C++ primer", 99.00, 6);
	Book book("C++ primer", 6, 99.00);
	int choice;
	cout << "1-->display the information of the book" << endl;
	cout << "2-->borrow book" << endl;
	cout << "3-->restore book" << endl;
	int contin = 1;
	while (contin)
	{
		cout << "Please input the function you want: ";
		cin >> choice;
		switch (choice)
		{
		case 1:book.Display(); break;
		case 2:book.Borrow(); break;
		case 3:book.Restore(); break;
		default:cout << "wrong operation!"; break;
		}
		cout << "continue? 1-->yes or 0-->no: ";
		cin >> contin;
	}
	return 0;
}

Answer 2

#include <iostream>
#include <string>
using namespace std;
class Book{
public:
Book(string mBookname,int mNumber,double mPrice);//这个构造函数参数数量声明与定义不一样，char是单个字符 应该改用string
void Display();
void Borrow();
void Restore();
friend double sum(Book &mNumber,Book &mPrice);//友元函数在定义的时候不加friend 就和普通函数一样定义
private:
string bookname;
double price;
int number;
};
Book::Book(string mBookname,int mNumber,double mPrice){
bookname=mBookname;
number=mNumber;
price=mPrice;
}
void Book::Display(){
cout<<"The bookname is "<<bookname<<" and its price is "<<price<<", we have"
<<number<<"of them."<<endl;
}
void Book::Borrow(){
number=number-1;
cout<<"We have"<<number<<"books left."<<endl;
}
void Book::Restore(){
number=number+1;
cout<<"We have "<<number<<"books left."<<endl;
}
int main()
{
Book book("C++ primer", 99.00, 6);
int choice;
cout << "1-->display the information of the book" << endl;
cout << "2-->borrow book" << endl;
cout << "3-->restore book" << endl;
int contin = 1;
while(contin)
{
cout << "Please input the function you want: ";
cin >> choice;
switch(choice)
{
case 1:book.Display();break;
case 2:book.Borrow();break;
case 3:book.Restore();break;
default:cout << "wrong operation!";break;
}
cout <<"continue? 1-->yes or 0-->no: ";
cin >> contin;
}
system("pause");
}
很不错的程序 问题不大