航班订票系统，录入航班，列出航班，在重新启动代码时还保存着上一次运行代码所录入的航班信息，c语言代码

下面是一个简单的基于文件存储的航班订票系统的C语言代码，可以实现录入航班、列出航班、保存航班信息和重新读取航班信息等功能。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_FLIGHTS 100

struct flight {
    char flight_num[10];    // 航班号
    char departure[20];     // 出发地
    char destination[20];   // 目的地
    int seats;              // 座位数
};

void save_flights(struct flight flights[], int num_flights) {
    FILE *fp = fopen("flights.dat", "wb");
    if (fp == NULL) {
        printf("Error: cannot open file.\n");
        return;
    }
    fwrite(flights, sizeof(struct flight), num_flights, fp);
    fclose(fp);
}

int load_flights(struct flight flights[]) {
    FILE *fp = fopen("flights.dat", "rb");
    if (fp == NULL) {
        return 0;
    }
    int num_flights = fread(flights, sizeof(struct flight), MAX_FLIGHTS, fp);
    fclose(fp);
    return num_flights;
}

void list_flights(struct flight flights[], int num_flights) {
    printf("Flight Number\tDeparture\tDestination\tSeats\n");
    printf("---------------------------------------------------\n");
    for (int i = 0; i < num_flights; i++) {
        printf("%s\t%s\t\t%s\t\t%d\n", flights[i].flight_num, flights[i].departure, flights[i].destination, flights[i].seats);
    }
}

void add_flight(struct flight flights[], int *num_flights) {
    if (*num_flights >= MAX_FLIGHTS) {
        printf("Error: too many flights.\n");
        return;
    }
    struct flight f;
    printf("Enter flight number: ");
    scanf("%s", f.flight_num);
    printf("Enter departure: ");
    scanf("%s", f.departure);
    printf("Enter destination: ");
    scanf("%s", f.destination);
    printf("Enter number of seats: ");
    scanf("%d", &f.seats);
    flights[*num_flights] = f;
    (*num_flights)++;
}

int main() {
    struct flight flights[MAX_FLIGHTS];
    int num_flights = load_flights(flights);
    char choice;
    do {
        printf("\nFlight Reservation System:\n");
        printf("1. List flights\n");
        printf("2. Add a flight\n");
        printf("3. Quit\n");
        printf("Enter choice: ");
        scanf(" %c", &choice);
        switch (choice) {
            case '1':
                list_flights(flights, num_flights);
                break;
            case '2':
                add_flight(flights, &num_flights);
                break;
            case '3':
                save_flights(flights, num_flights);
                printf("Exiting...\n");
                break;
            default:
                printf("Invalid choice. Try again.\n");
        }
    } while (choice != '3');
    return 0;
}

在程序启动时，我们先调用`load_flights`函数从文件中读取保存的航班信息。在录入新的航班信息时，将其添加到`flights`数组中，同时更新`num_flights`变量来记录航班数量。在程序退出前，我们调用`save_flights`函数将`flights`数组中的航班信息写入文件中，以便下次启动程序时可以重新读取。