图书管理系统（第一版C++文件操作）

功能

录入书籍，删除书籍，查询书籍，借书，还书

但是录入书籍存在重复情况，无法修改数目

#include<iostream>
using namespace std;
#include<fstream>
#define filename "booklist.txt"
#include<list>
#include<cstring>
#include<iomanip>

class Book    //创建Book类，存放图书信息
{
public:
    Book(string na=" ", int p=0, int n=0)
    {
        name = na;
        num = n;
        price = p;
    }
    void Show()
    {
        cout <<  "书名：" << std::left << setw(20) << name << std::right << setw(6) << "\t价格：" << price << "\t数量：" << num << endl;
    }
    void Set()
    {
        cout << "请输入书名:";
        cin >> name;
        cout << "请输入价格:";
        cin >> price;
        cout << "请输入数量:";
        cin >> num;
    }
    void Addnum()
    {
        int n;
        cout << "请输入归还的数量：";
        cin >> n;
        num += n;
    }
    void Borrownum()
    {
        int n;
        cout << "请输入借出的数量：";
        cin >> n;
        num -= n;
    }
public:
    string name;
    int price;
    int num;
};

void menu()
{
    cout << "--------------------------------------欢迎进入图书管理系统--------------------------------------" << endl;
    cout << endl << "0 - 退出系统；" << "1 - 显示库存；" << "2 - 查询图书；" << "3 - 借阅图书；" << "4 - 归还图书；" << "5 - 增加图书；" << "6 - 删除图书；" << endl;
}

class Booklist    //创建BookList类，数据成员有Book还有图书数量
{
public:
    void save()    //新建图书的话保存数据，用app方式打开文件
    {
        ofstream fout(filename, ios::app);
        list<Book>::iterator it = BList.begin();
        for (int i = 0; i < num-1; i++)    //偏移迭代器，指向新加入的Book并写入文件
        {
            it++;
        }
        for (; it != BList.end(); it++)
        {
            fout << (*it).name << ' ' << (*it).price << ' ' << (*it).num << '\n';
        }
        fout.close();
    }
    void resave()
    {
        ofstream fout(filename, ios::out);    //重新写入数据，因为删除了某个元素
        if (fout.is_open())
        {
            for (list<Book>::iterator it = BList.begin(); it != BList.end(); it++)
            {
                fout << (*it).name << ' ' << (*it).price << ' ' << (*it).num << '\n';
            }
        }
        fout.close();
    }
    void Show()
    {
        for (list<Book>::iterator it = BList.begin(); it != BList.end(); it++)
        {
            (*it).Show();
        }
    }
    void adddata()    //添加数据
    {
        Book B;
        B.Set();
        BList.push_back(B);
        num++;
    }
    void start()    //程序一开始读取文件里的数据
    {
        string na;
        int n;
        int p;
        ifstream fin(filename, ios::in);
        if (fin.is_open())
        {
            while (fin >> na >> p >> n)
            {
                Book B(na, p, n);
                BList.push_back(B);
                num++;
            }
        }
        fin.close();
    }
    void increase()
    {
        cout << "请输入书名：" << endl;
        string n;
        cin >> n;
        for (list<Book>::iterator it = BList.begin(); it != BList.end(); it++)
        {
            if ((*it).name == n)
                (*it).Addnum();
        }
        resave();
    }
    void decrease()
    {
        cout << "请输入书名：" << endl;
        string n;
        cin >> n;
        for (list<Book>::iterator it = BList.begin(); it != BList.end(); it++)
        {
            if ((*it).name == n)
                (*it).Borrownum();
        }
        resave();
    }
    void FindBook()
    {
        string name;
        cin >> name;
        for (list<Book>::iterator it = BList.begin(); it != BList.end(); it++)    //遍历整个list，所以符合关键字的都会被找到
        {
            int index = (*it).name.find(name);    //如果没找到返回值是一个很大的数
            if (index < (*it).name.length())
                (*it).Show();
        }
    }
    void DeleteBook()
    {
        string name;
        cout << "请输入书名：";
        cin >> name;
        int i = 0;
        for (list<Book>::iterator it = BList.begin(); it != BList.end();it++)
        {
            if ((*it).name == name)
                break;
            ++i;
        }
        list<Book>::iterator it = BList.begin();
        advance(it, i);
        BList.erase(it);
        --num;
        resave();
    }
public:
    list<Book>BList;
    int num = 0;
};

int main()
{
    Booklist B1;
    B1.start();
    while (1)
    {
        menu();
        int key;
        cout << "请输入要进行的操作：";
        cin >> key;
        switch (key)
        {
        case 0:
            return 0;
            break;
        case 1:
            B1.Show();
            break;
        case 2:
            B1.FindBook();
            break;
        case 3:
            B1.decrease();
            break;
        case 4:
            B1.increase();
            break;
        case 5:
        {
            B1.adddata();
            B1.save();
            break;
        }
        case 6:
            B1.DeleteBook();
            break;
        }

    }
}