你可以用c++帮我写一个简单的快件管理系统吗，要求进入系统后首先选择取件人模式或管理员模式，内置管理员的账号密码，取件人可以凭借手机号或者快递单号取快递，管理员可以进行快件的录入，删除，读取，修改，查询已取快件，查询未取快件，一个快件应包含的信息有：随机生成的快递单号，寄件人，寄件人手机号，寄件人住址，收件人，收件人手机号，收件人住址。退出系统时回到选择模式的界面。400行以上代码

好的，下面是使用 C++ 实现的一个简单的快件管理系统，包含取件人模式和管理员模式，内置管理员账号密码，取件人可以凭手机号或快递单号取快递，管理员可以进行快件的录入、删除、读取、修改，以及查询已取快件和未取快件。

在本示例中，一个快件包含的信息有：快递单号、寄件人、寄件人手机号、寄件人住址、收件人、收件人手机号、收件人住址。

代码如下：

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
#include <ctime>

using namespace std;

// 定义一个全局变量，用来存储快递信息
vector< vector<string> > express_list;

// 生成指定长度的随机字符串
string random_string(int length) {
    static const string charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
    string result;
    result.resize(length);
    srand(time(0));
    for (int i = 0; i < length; i++) {
        result[i] = charset[rand() % charset.length()];
    }
    return result;
}

// 查询快递信息
void query_express() {
    string query_type;
    cout << "请选择查询方式(1. 按手机号查询，2. 按快递单号查询): ";
    cin >> query_type;
    while (query_type != "1" && query_type != "2") {
        cout << "输入有误，请重新输入！" << endl;
        cout << "请选择查询方式(1. 按手机号查询，2. 按快递单号查询): ";
        cin >> query_type;
    }
    string query_value;
    cout << "请输入查询值: ";
    cin >> query_value;
    bool found = false;
    for (int i = 0; i < express_list.size(); i++) {
        if (query_type == "1" && express_list[i][2] == query_value) {
            found = true;
            cout << "快递单号：" << express_list[i][0] << endl;
            cout << "寄件人：" << express_list[i][1] << endl;
            cout << "寄件人手机号：" << express_list[i][2] << endl;
            cout << "寄件人住址：" << express_list[i][3] << endl;
            cout << "收件人：" << express_list[i][4] << endl;
            cout << "收件人手机号：" << express_list[i][5] << endl;
            cout << "收件人住址：" << express_list[i][6] << endl;
            cout << endl;
        }
        if (query_type == "2" && express_list[i][0] == query_value) {
            found = true;
            cout << "快递单号：" << express_list[i][0] << endl;
            cout << "寄件人：" << express_list[i][1] << endl;
            cout << "寄件人手机号：" << express_list[i][2] << endl;
            cout << "寄件人住址：" << express_list[i][3] << endl;
            cout << "收件人：" << express_list[i][4] << endl;
            cout << "收件人手机号：" << express_list[i][5] << endl;
            cout << "收件人住址：" << express_list[i][6] << endl;
            cout << endl;
        }
    }
    if (!found) {
        cout << "未找到符合条件的快递信息！" << endl;
    }
}

// 录入快递信息
void add_express() {
    vector<string> express;
    express.push_back(random_string(10)); // 生成10位随机快递单号
    cout << "请输入寄件人姓名: ";
    string sender_name;
    cin >> sender_name;
    express.push_back(sender_name);
    cout << "请输入寄件人手机号: ";
    string sender_phone_number;
    cin >> sender_phone_number;
    express.push_back(sender_phone_number);
    cout << "请输入寄件人住址: ";
    string sender_address;
    cin >> sender_address;
    express.push_back(sender_address);
    cout << "请输入收件人姓名: ";
    string receiver_name;
    cin >> receiver_name;
    express.push_back(receiver_name);
    cout << "请输入收件人手机号: ";
    string receiver_phone_number;
    cin >> receiver_phone_number;
    express.push_back(receiver_phone_number);
    cout << "请输入收件人住址: ";
    string receiver_address;
    cin >> receiver_address;
    express.push_back(receiver_address);
    express_list.push_back(express);
    cout << "快递信息录入成功！" << endl;
}

// 删除快递信息
void delete_express() {
    string express_id;
    cout << "请输入要删除的快递单号: ";
    cin >> express_id;
    bool found = false;
    for (int i = 0; i < express_list.size(); i++) {
        if (express_list[i][0] == express_id) {
            found = true;
            express_list.erase(express_list.begin() + i);
            cout << "快递信息删除成功！" << endl;
            break;
        }
    }
    if (!found) {
        cout << "未找到符合条件的快递信息！" << endl;
    }
}

// 修改快递信息
void modify_express() {
    string express_id;
    cout << "请输入要修改的快递单号: ";
    cin >> express_id;
    bool found = false;
    for (int i = 0; i < express_list.size(); i++) {
        if (express_list[i][0] == express_id) {
            found = true;
            cout << "请输入寄件人姓名(" << express_list[i][1] << "): ";
            string sender_name;
            cin >> sender_name;
            express_list[i][1] = sender_name;
            cout << "请输入寄件人手机号(" << express_list[i][2] << "): ";
            string sender_phone_number;
            cin >> sender_phone_number;
            express_list[i][2] = sender_phone_number;
            cout << "请输入寄件人住址(" << express_list[i][3] << "): ";
            string sender_address;
            cin >> sender_address;
            express_list[i][3] = sender_address;
            cout << "请输入收件人姓名(" << express_list[i][4] << "): ";
            string receiver_name;
            cin >> receiver_name;
            express_list[i][4] = receiver_name;
            cout << "请输入收件人手机号(" << express_list[i][5] << "): ";
            string receiver_phone_number;
            cin >> receiver_phone_number;
            express_list[i][5] = receiver_phone_number;
            cout << "请输入收件人住址(" << express_list[i][6] << "): ";
            string receiver_address;
            cin >> receiver_address;
            express_list[i][6] = receiver_address;
            cout << "快递信息修改成功！" << endl;
            break;
        }
    }
    if (!found) {
        cout << "未找到符合条件的快递信息！" << endl;
    }
}

// 查询已取快件
void query_taken_express() {
    bool found = false;
    for (int i = 0; i < express_list.size(); i++) {
        if (express_list[i].size() > 7 && express_list[i][7] == "1") {
            found = true;
            cout << "快递单号：" << express_list[i][0] << endl;
            cout << "寄件人：" << express_list[i][1] << endl;
            cout << "寄件人手机号：" << express_list[i][2] << endl;
            cout << "寄件人住址：" << express_list[i][3] << endl;
            cout << "收件人：" << express_list[i][4] << endl;
            cout << "收件人手机号：" << express_list[i][5] << endl;
            cout << "收件人住址：" << express_list[i][6] << endl;
            cout << endl;
        }
    }
    if (!found) {
        cout << "未找到已取快件信息！" << endl;
    }
}

// 查询未取快件
void query_untaken_express() {
    bool found = false;
    for (int i = 0; i < express_list.size(); i++) {
        if (express_list[i].size() <= 7 || express_list[i][7] == "0") {
            found = true;
            cout << "快递单号：" << express_list[i][0] << endl;
            cout << "寄件人：" << express_list[i][1] << endl;
            cout << "寄件人手机号：" << express_list[i][2] << endl;
            cout << "寄件人住址：" << express_list[i][3] << endl;
            cout << "收件人：" << express_list[i][4] << endl;
            cout << "收件人手机号：" << express_list[i][5] << endl;
            cout << "收件人住址：" << express_list[i][6] << endl;
            cout << endl;
        }
    }
    if (!found) {
        cout << "未找到未取快件信息！" << endl;
    }
}

// 管理员模式
void admin_mode() {
    string username;
    string password;
    cout << "请输入管理员账号: ";
    cin >> username;
    cout << "请输入管理员密码: ";
    cin >> password;
    if (username != "admin" || password != "123456") {
        cout << "管理员账号或密码错误！" << endl;
        return;
    }
    string choice;
    do {
        cout << "请选择操作(1. 录入快递，2. 删除快递，3. 修改快递，4. 查询已取快件，5. 查询未取快件，6. 返回主菜单): ";
        cin >> choice;
        while (choice != "1" && choice != "2" && choice != "3" && choice != "4" && choice != "5" && choice != "6") {
            cout << "输入有误，请重新输入！" << endl;
            cout << "请选择操作(1. 录入快递，2. 删除快