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，设计Book类，Patron类,Date类

以下是多文件程序的代码实现：

首先是Date类的头文件 Date.h：

#ifndef DATE_H
#define DATE_H

class Date {
private:
    int year, month, day;
public:
    Date(int y, int m, int d);
    int getYear() const;
    int getMonth() const;
    int getDay() const;
};

#endif

Date类的实现文件 Date.cpp:

#include "Date.h"

Date::Date(int y, int m, int d) {
    year = y;
    month = m;
    day = d;
}

int Date::getYear() const {
    return year;
}

int Date::getMonth() const {
    return month;
}

int Date::getDay() const {
    return day;
}

接下来是Book类的头文件 Book.h：

#ifndef BOOK_H
#define BOOK_H

#include <string>

class Book {
private:
    std::string title;
    std::string author;
    std::string isbn;
    bool is_available;
public:
    Book(std::string t, std::string a, std::string i);
    std::string getTitle() const;
    std::string getAuthor() const;
    std::string getIsbn() const;
    bool getAvailability() const;
    void setAvailability(bool b);
};

#endif

Book类的实现文件 Book.cpp:

#include "Book.h"

Book::Book(std::string t, std::string a, std::string i) {
    title = t;
    author = a;
    isbn = i;
    is_available = true;
}

std::string Book::getTitle() const {
    return title;
}

std::string Book::getAuthor() const {
    return author;
}

std::string Book::getIsbn() const {
    return isbn;
}

bool Book::getAvailability() const {
    return is_available;
}

void Book::setAvailability(bool b) {
    is_available = b;
}

接下来是Patron类的头文件 Patron.h：

#ifndef PATRON_H
#define PATRON_H

#include <string>

class Patron {
private:
    std::string name;
    double fees;
public:
    Patron(std::string n);
    std::string getName() const;
    double getFees() const;
    void addFee(double f);
};

#endif

Patron类的实现文件 Patron.cpp：

#include "Patron.h"

Patron::Patron(std::string n) {
    name = n;
    fees = 0.0;
}

std::string Patron::getName() const {
    return name;
}

double Patron::getFees() const {
    return fees;
}

void Patron::addFee(double f) {
    fees += f;
}

最后是Library类的头文件 Library.h：

#ifndef LIBRARY_H
#define LIBRARY_H

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

struct Transaction {
    Book book;
    Patron patron;
    Date date;
};

class Library {
private:
    std::vector<Book> books;
    std::vector<Patron> patrons;
    std::vector<Transaction> transactions;
public:
    void addBook(Book b);
    void addPatron(Patron p);
    void lendBook(Book b, Patron p, Date d);
    std::vector<std::string> getDebtors() const;
};

#endif

Library类的实现文件 Library.cpp：

#include "Library.h"

void Library::addBook(Book b) {
    books.push_back(b);
}

void Library::addPatron(Patron p) {
    patrons.push_back(p);
}

void Library::lendBook(Book b, Patron p, Date d) {
    bool book_found = false;
    bool patron_found = false;
    int book_index = 0;
    int patron_index = 0;

    // Check if book exists
    for (int i = 0; i < books.size(); i++) {
        if (books[i].getIsbn() == b.getIsbn()) {
            book_found = true;
            book_index = i;
            break;
        }
    }

    // Check if patron exists
    for (int i = 0; i < patrons.size(); i++) {
        if (patrons[i].getName() == p.getName()) {
            patron_found = true;
            patron_index = i;
            break;
        }
    }

    // If book or patron not found, report error
    if (!book_found || !patron_found) {
        std::cout << "Error: book or patron not found" << std::endl;
        return;
    }

    // Check if book is available
    if (!books[book_index].getAvailability()) {
        std::cout << "Error: book is not available" << std::endl;
        return;
    }

    // Check if patron owes fees
    if (patrons[patron_index].getFees() > 0.0) {
        std::cout << "Error: patron owes fees" << std::endl;
        return;
    }

    // Lend book and record transaction
    books[book_index].setAvailability(false);
    Transaction t = { b, p, d };
    transactions.push_back(t);
}

std::vector<std::string> Library::getDebtors() const {
    std::vector<std::string> debtors;
    for (int i = 0; i < patrons.size(); i++) {
        if (patrons[i].getFees() > 0.0) {
            debtors.push_back(patrons[i].getName());
        }
    }
    return debtors;
}

最后是主测试文件 main.cpp，包含一个简单的菜单：

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

int main() {
    Library library;

    while (true) {
        std::cout << "1. Add book" << std::endl;
        std::cout << "2. Add patron" << std::endl;
        std::cout << "3. Lend book" << std::endl;
        std::cout << "4. List debtors" << std::endl;
        std::cout << "5. Exit" << std::endl;
        std::cout << "Enter choice: ";
        int choice;
        std::cin >> choice;

        if (choice == 1) {
            std::cout << "Enter title: ";
            std::string title;
            std::cin >> title;
            std::cout << "Enter author: ";
            std::string author;
            std::cin >> author;
            std::cout << "Enter ISBN: ";
            std::string isbn;
            std::cin >> isbn;
            Book book(title, author, isbn);
            library.addBook(book);
            std::cout << "Book added" << std::endl;
        }
        else if (choice == 2) {
            std::cout << "Enter name: ";
            std::string name;
            std::cin >> name;
            Patron patron(name);
            library.addPatron(patron);
            std::cout << "Patron added" << std::endl;
        }
        else if (choice == 3) {
            std::cout << "Enter ISBN: ";
            std::string isbn;
            std::cin >> isbn;
            Book book("", "", isbn);
            std::cout << "Enter patron name: ";
            std::string name;
            std::cin >> name;
            Patron patron(name);
            std::cout << "Enter date (year month day): ";
            int year, month, day;
            std::cin >> year >> month >> day;
            Date date(year, month, day);
            library.lendBook(book, patron, date);
        }
        else if (choice == 4) {
            std::vector<std::string> debtors = library.getDebtors();
            if (debtors.size() == 0) {
                std::cout << "No debtors" << std::endl;
            }
            else {
                std::cout << "Debtors:" << std::endl;
                for (int i = 0; i < debtors.size(); i++) {
                    std::cout << debtors[i] << std::endl;
                }
            }
        }
        else if (choice == 5) {
            break;
        }
    }

    return 0;
}