1）录入航线信息，每条航线信息包括航班号、飞机号、目的地、订票数、余票数共5项。
2）订票业务，每个客户包括姓名, 航班号, 座位号(初始为0)。
3）退票业务，根据客户提出的航班号, 办理退票。
4）修改航班信息，当航班信息改变可以修改航班数据文件。（客户无法修改）
输出航线信息和客户信息。(1) enter the route information, each flight information includes flight number, aircraft number, destination, booking number, and the total number of votes in 5.
2) booking business, each customer including name, flight number, seat number (initial 0).
3) refund business, according to the customer's flight number, refund.
4) modify flight information, when the flight information changes, you can modify the flight data file. (customer cannot modify)
Output airline information and customer information.)