创建一个 Library类，包含一个 Book向量和一个Patron向量。定义一个名为Transaction 的 struet，包含一个Book对象、一个Patron对象和一个本章中定义的Date对象，表示借阅记录。在 Library 类中定义一个Transaction向量。定义向图书馆添加图书、添加读者以及借出书籍的函数。当一个读者借出一本书时,保证Library对象中有此读者和这本书的记录,否则报告错误。然后检查读者是否欠费，如果欠费就报告一个错误,否则创建一个Transaction对象，将其放人Transaction向量中。定义一个返回包含所有欠费读者姓名的向量的函数。该软件是多文件程序，按文件给出代码，在主测试文件中设置菜单，由用户手动录入图书信息，用C++设计实现，只需要写出主测试文件

主测试文件代码如下：

#include <iostream>
#include <vector>
#include "Library.h"

using namespace std;

void displayMenu();

int main() {
    Library library;
    int choice;

    do {
        displayMenu();
        cin >> choice;

        switch (choice) {
            case 1:
                // 添加图书
                cout << "请输入图书信息：" << endl;
                library.addBook();
                break;
            case 2:
                // 添加读者
                cout << "请输入读者信息：" << endl;
                library.addPatron();
                break;
            case 3:
                // 借出书籍
                library.checkoutBook();
                break;
            case 4:
                // 欠费读者
                vector<string> debtors = library.getDebtors();
                if (debtors.empty()) {
                    cout << "目前没有欠费读者" << endl;
                } else {
                    cout << "欠费读者：" << endl;
                    for (string debtor : debtors) {
                        cout << debtor << endl;
                    }
                }
                break;
            case 0:
                cout << "谢谢使用！" << endl;
                break;
            default:
                cout << "输入错误，请重新输入" << endl;
                break;
        }
    } while (choice != 0);

    return 0;
}

void displayMenu() {
    cout << "请选择操作：" << endl;
    cout << "1. 添加图书" << endl;
    cout << "2. 添加读者" << endl;
    cout << "3. 借出书籍" << endl;
    cout << "4. 查询欠费读者" << endl;
    cout << "0. 退出" << endl;
}

Library.h 头文件代码如下：

#ifndef LIBRARY_H
#define LIBRARY_H

#include <vector>
#include "Book.h"
#include "Patron.h"
#include "Transaction.h"

class Library {
public:
    void addBook();
    void addPatron();
    void checkoutBook();
    std::vector<std::string> getDebtors();

private:
    std::vector<Book> books;
    std::vector<Patron> patrons;
    std::vector<Transaction> transactions;

    bool hasBook(const Book& book) const;
    bool hasPatron(const Patron& patron) const;
    bool hasTransaction(const Transaction& transaction) const;
    bool isPatronInDebt(const Patron& patron) const;
};

#endif

Library.cpp 源文件代码如下：

#include <iostream>
#include <algorithm>
#include "Library.h"

using namespace std;

void Library::addBook() {
    Book book;
    cin >> book;
    books.push_back(book);
    cout << "添加成功！" << endl;
}

void Library::addPatron() {
    Patron patron;
    cin >> patron;
    patrons.push_back(patron);
    cout << "添加成功！" << endl;
}

void Library::checkoutBook() {
    Book book;
    Patron patron;
    Date date;

    cout << "请输入借阅信息：" << endl;
    cout << "图书信息：" << endl;
    cin >> book;
    cout << "读者信息：" << endl;
    cin >> patron;
    cout << "借阅日期（年 月 日）：" << endl;
    cin >> date;

    if (!hasBook(book)) {
        cout << "图书不存在" << endl;
        return;
    }

    if (!hasPatron(patron)) {
        cout << "读者不存在" << endl;
        return;
    }

    if (isPatronInDebt(patron)) {
        cout << "读者欠费，无法借阅" << endl;
        return;
    }

    Transaction transaction{book, patron, date};
    transactions.push_back(transaction);
    cout << "借阅成功！" << endl;
}

vector<string> Library::getDebtors() {
    vector<string> debtors;

    for (Patron patron : patrons) {
        if (patron.getFee() > 0) {
            debtors.push_back(patron.getName());
        }
    }

    return debtors;
}

bool Library::hasBook(const Book& book) const {
    auto it = find(books.begin(), books.end(), book);
    return it != books.end();
}

bool Library::hasPatron(const Patron& patron) const {
    auto it = find(patrons.begin(), patrons.end(), patron);
    return it != patrons.end();
}

bool Library::hasTransaction(const Transaction& transaction) const {
    auto it = find(transactions.begin(), transactions.end(), transaction);
    return it != transactions.end();
}

bool Library::isPatronInDebt(const Patron& patron) const {
    return patron.getFee() > 0;
}

Book.h 头文件代码如下：

#ifndef BOOK_H
#define BOOK_H

#include <string>

class Book {
public:
    Book() = default;
    Book(const std::string& isbn, const std::string& title, const std::string& author);

    std::string getISBN() const { return isbn; }
    std::string getTitle() const { return title; }
    std::string getAuthor() const { return author; }

    friend bool operator==(const Book& lhs, const Book& rhs);
    friend std::istream& operator>>(std::istream& is, Book& book);

private:
    std::string isbn;
    std::string title;
    std::string author;
};

#endif

Book.cpp 源文件代码如下：

#include <iostream>
#include "Book.h"

using namespace std;

Book::Book(const string& isbn, const string& title, const string& author)
    : isbn(isbn), title(title), author(author) {}

bool operator==(const Book& lhs, const Book& rhs) {
    return lhs.isbn == rhs.isbn;
}

istream& operator>>(istream& is, Book& book) {
    cout << "ISBN: ";
    getline(is, book.isbn);
    cout << "书名: ";
    getline(is, book.title);
    cout << "作者: ";
    getline(is, book.author);
    return is;
}

Patron.h 头文件代码如下：

#ifndef PATRON_H
#define PATRON_H

#include <string>

class Patron {
public:
    Patron() = default;
    Patron(const std::string& name, const std::string& id);

    std::string getName() const { return name; }
    std::string getId() const { return id; }
    double getFee() const { return fee; }
    void addFee(double amount) { fee += amount; }

    friend bool operator==(const Patron& lhs, const Patron& rhs);
    friend std::istream& operator>>(std::istream& is, Patron& patron);

private:
    std::string name;
    std::string id;
    double fee = 0.0;
};

#endif

Patron.cpp 源文件代码如下：

#include <iostream>
#include "Patron.h"

using namespace std;

Patron::Patron(const string& name, const string& id)
    : name(name), id(id) {}

bool operator==(const Patron& lhs, const Patron& rhs) {
    return lhs.id == rhs.id;
}

istream& operator>>(istream& is, Patron& patron) {
    cout << "姓名: ";
    getline(is, patron.name);
    cout << "ID: ";
    getline(is, patron.id);
    return is;
}

Transaction.h 头文件代码如下：

#ifndef TRANSACTION_H
#define TRANSACTION_H

#include "Book.h"
#include "Patron.h"
#include "Date.h"

class Transaction {
public:
    Transaction() = default;
    Transaction(const Book& book, const Patron& patron, const Date& date);

    Book getBook() const { return book; }
    Patron getPatron() const { return patron; }
    Date getDate() const { return date; }

private:
    Book book;
    Patron patron;
    Date date;
};

#endif

Transaction.cpp 源文件代码如下：

#include "Transaction.h"

Transaction::Transaction(const Book& book, const Patron& patron, const Date& date)
    : book(book), patron(patron), date(date) {}