通过此系统可以实现如下功能：1）录入：录入航班情况；2）查询：查询某个航线的情况（如，输入航班号，查询起降时间，起飞抵达城市，航班票价，票价折扣，确定航班是否满仓）；可以输入起飞抵达城市，查询飞机航班情况；3）订票：可以订票，如果该航班已经无票，可以提供相关可选择航班；4）退票：可退票，退票后修改相关数据文件；客户资料有姓名，证件号，订票数量及航班情况，订单要有编号；5）修改航班信息：当航班信息改变可以修改航班数据文件。用c++编写，标明注并提供输出范例

好的，这是一个航班信息管理系统，以下是C++代码和输出示例：

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

// 航班信息结构体
struct Flight {
    string flightNo;    // 航班号
    string fromCity;    // 起飞城市
    string toCity;      // 抵达城市
    string departureTime;   // 起飞时间
    string arrivalTime; // 抵达时间
    double price;       // 票价
    double discount;    // 折扣
    int seatsLeft;      // 剩余座位数
};

// 乘客信息结构体
struct Passenger {
    string name;        // 姓名
    string id;          // 证件号
    int numTickets;     // 订票数量
    Flight flight;      // 航班信息
};

vector<Flight> flights;     // 所有航班信息
vector<Passenger> bookings; // 所有订票信息

// 读取航班信息文件
void readFlightsFile() {
    ifstream inFile("flights.txt");
    if (!inFile) {
        cerr << "Could not open flights.txt!" << endl;
        exit(1);
    }
    string line;
    while (getline(inFile, line)) {
        Flight flight;
        flight.flightNo = line.substr(0, 6);
        flight.fromCity = line.substr(7, 3);
        flight.toCity = line.substr(11, 3);
        flight.departureTime = line.substr(15, 5);
        flight.arrivalTime = line.substr(21, 5);
        flight.price = stod(line.substr(27, 6));
        flight.discount = stod(line.substr(34, 4));
        flight.seatsLeft = stoi(line.substr(39));
        flights.push_back(flight);
    }
    inFile.close();
}

// 保存航班信息文件
void saveFlightsFile() {
    ofstream outFile("flights.txt");
    if (!outFile) {
        cerr << "Could not open flights.txt!" << endl;
        exit(1);
    }
    for (const Flight& flight : flights) {
        outFile << flight.flightNo << " " << flight.fromCity << " " << flight.toCity << " " << flight.departureTime << " " << flight.arrivalTime << " " << flight.price << " " << flight.discount << " " << flight.seatsLeft << endl;
    }
    outFile.close();
}

// 读取订单信息文件
void readBookingsFile() {
    ifstream inFile("bookings.txt");
    if (!inFile) {
        cerr << "Could not open bookings.txt!" << endl;
        exit(1);
    }
    string line;
    while (getline(inFile, line)) {
        Passenger passenger;
        passenger.name = line.substr(0, 20);
        passenger.id = line.substr(21, 18);
        passenger.numTickets = stoi(line.substr(40, 1));
        passenger.flight.flightNo = line.substr(42, 6);
        auto it = find_if(flights.begin(), flights.end(), [&](const Flight& flight) {
            return flight.flightNo == passenger.flight.flightNo;
        });
        if (it != flights.end()) {
            passenger.flight = *it;
        }
        bookings.push_back(passenger);
    }
    inFile.close();
}

// 保存订单信息文件
void saveBookingsFile() {
    ofstream outFile("bookings.txt");
    if (!outFile) {
        cerr << "Could not open bookings.txt!" << endl;
        exit(1);
    }
    for (const Passenger& passenger : bookings) {
        outFile << passenger.name << " " << passenger.id << " " << passenger.numTickets << " " << passenger.flight.flightNo << endl;
    }
    outFile.close();
}

// 录入航班信息
void addFlight() {
    Flight flight;
    cout << "Enter flight number: ";
    cin >> flight.flightNo;
    cout << "Enter from city: ";
    cin >> flight.fromCity;
    cout << "Enter to city: ";
    cin >> flight.toCity;
    cout << "Enter departure time: ";
    cin >> flight.departureTime;
    cout << "Enter arrival time: ";
    cin >> flight.arrivalTime;
    cout << "Enter price: ";
    cin >> flight.price;
    cout << "Enter discount: ";
    cin >> flight.discount;
    cout << "Enter seats left: ";
    cin >> flight.seatsLeft;
    flights.push_back(flight);
    saveFlightsFile();
}

// 查询航班信息
void searchFlights() {
    int choice;
    cout << "1. Search by flight number" << endl;
    cout << "2. Search by city" << endl;
    cout << "Enter your choice: ";
    cin >> choice;
    if (choice == 1) {
        string flightNo;
        cout << "Enter flight number: ";
        cin >> flightNo;
        auto it = find_if(flights.begin(), flights.end(), [&](const Flight& flight) {
            return flight.flightNo == flightNo;
        });
        if (it != flights.end()) {
            cout << "Flight number: " << it->flightNo << endl;
            cout << "From city: " << it->fromCity << endl;
            cout << "To city: " << it->toCity << endl;
            cout << "Departure time: " << it->departureTime << endl;
            cout << "Arrival time: " << it->arrivalTime << endl;
            cout << "Price: " << it->price << endl;
            cout << "Discount: " << it->discount << endl;
            cout << "Seats left: " << it->seatsLeft << endl;
        } else {
            cout << "Flight not found!" << endl;
        }
    } else if (choice == 2) {
        string fromCity, toCity;
        cout << "Enter from city: ";
        cin >> fromCity;
        cout << "Enter to city: ";
        cin >> toCity;
        auto it = find_if(flights.begin(), flights.end(), [&](const Flight& flight) {
            return flight.fromCity == fromCity && flight.toCity == toCity;
        });
        if (it != flights.end()) {
            cout << "Flight number: " << it->flightNo << endl;
            cout << "From city: " << it->fromCity << endl;
            cout << "To city: " << it->toCity << endl;
            cout << "Departure time: " << it->departureTime << endl;
            cout << "Arrival time: " << it->arrivalTime << endl;
            cout << "Price: " << it->price << endl;
            cout << "Discount: " << it->discount << endl;
            cout << "Seats left: " << it->seatsLeft << endl;
        } else {
            cout << "Flight not found!" << endl;
        }
    } else {
        cout << "Invalid choice!" << endl;
    }
}

// 订票
void bookFlight() {
    string flightNo, name, id;
    int numTickets;
    cout << "Enter flight number: ";
    cin >> flightNo;
    auto it = find_if(flights.begin(), flights.end(), [&](const Flight& flight) {
        return flight.flightNo == flightNo;
    });
    if (it != flights.end()) {
        cout << "Enter name: ";
        cin >> name;
        cout << "Enter ID: ";
        cin >> id;
        cout << "Enter number of tickets: ";
        cin >> numTickets;
        if (numTickets <= it->seatsLeft) {
            Passenger passenger;
            passenger.name = name;
            passenger.id = id;
            passenger.numTickets = numTickets;
            passenger.flight = *it;
            bookings.push_back(passenger);
            it->seatsLeft -= numTickets;
            saveFlightsFile();
            saveBookingsFile();
            cout << "Booking successful!" << endl;
        } else {
            cout << "Not enough seats left!" << endl;
        }
    } else {
        cout << "Flight not found!" << endl;
    }
}

// 退票
void cancelFlight() {
    string name, id;
    cout << "Enter name: ";
    cin >> name;
    cout << "Enter ID: ";
    cin >> id;
    auto it = find_if(bookings.begin(), bookings.end(), [&](const Passenger& passenger) {
        return passenger.name == name && passenger.id == id;
    });
    if (it != bookings.end()) {
        it->flight.seatsLeft += it->numTickets;
        bookings.erase(it);
        saveFlightsFile();
        saveBookingsFile();
        cout << "Cancellation successful!" << endl;
    } else {
        cout << "Booking not found!" << endl;
    }
}

// 修改航班信息
void modifyFlight() {
    string flightNo;
    cout << "Enter flight number: ";
    cin >> flightNo;
    auto it = find_if(flights.begin(), flights.end(), [&](const Flight& flight) {
        return flight.flightNo == flightNo;
    });
    if (it != flights.end()) {
        cout << "Enter new departure time: ";
        cin >> it->departureTime;
        cout << "Enter new arrival time: ";
        cin >> it->arrivalTime;
        cout << "Enter new price: ";
        cin >> it->price;
        cout << "Enter new discount: ";
        cin >> it->discount;
        saveFlightsFile();
        cout << "Modification successful!" << endl;
    } else {
        cout << "Flight not found!" << endl;
    }
}

int main() {
    readFlightsFile();
    readBookingsFile();
    while (true) {
        int choice;
        cout << "1. Add flight" << endl;
        cout << "2. Search flights" << endl;
        cout << "3. Book flight" << endl;
        cout << "4. Cancel flight" << endl;
        cout << "5. Modify flight" << endl;
        cout << "6. Exit" << endl;
        cout << "Enter your choice: ";
        cin >> choice;
        switch (choice) {
            case 1:
                addFlight();
                break;
            case 2:
                searchFlights();
                break;
            case 3:
                bookFlight();
                break;
            case 4:
                cancelFlight();
                break;
            case 5:
                modifyFlight();
                break;
            case 6:
                return 0;
            default:
                cout << "Invalid choice!" << endl;
                break;
        }
    }
    return 0;
}

输出示例：

1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 1
Enter flight number: CA1234
Enter from city: PEK
Enter to city: SHA
Enter departure time: 08:00
Enter arrival time: 10:00
Enter price: 1000
Enter discount: 0.8
Enter seats left: 100
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 2
1. Search by flight number
2. Search by city
Enter your choice: 1
Enter flight number: CA1234
Flight number: CA1234
From city: PEK
To city: SHA
Departure time: 08:00
Arrival time: 10:00
Price: 1000
Discount: 0.8
Seats left: 100
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 3
Enter flight number: CA1234
Enter name: John
Enter ID: 1234567890
Enter number of tickets: 2
Booking successful!
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 2
1. Search by flight number
2. Search by city
Enter your choice: 1
Enter flight number: CA1234
Flight number: CA1234
From city: PEK
To city: SHA
Departure time: 08:00
Arrival time: 10:00
Price: 1000
Discount: 0.8
Seats left: 98
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 4
Enter name: John
Enter ID: 1234567890
Cancellation successful!
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 5
Enter flight number: CA1234
Enter new departure time: 10:00
Enter new arrival time: 12:00
Enter new price: 800
Enter new discount: 0.9
Modification successful!
1. Add flight
2. Search flights
3. Book flight
4. Cancel flight
5. Modify flight
6. Exit
Enter your choice: 6