航班订票系统，查询航班信息，订票，退票，C语言代码

以下是一个简单的航班订票系统的 C 语言代码示例：

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

#define MAX_FLIGHTS 10
#define MAX_NAME_LENGTH 30

typedef struct {
    char from[MAX_NAME_LENGTH];
    char to[MAX_NAME_LENGTH];
    int seats;
    int price;
} Flight;

Flight flights[MAX_FLIGHTS];
int num_flights = 0;

void add_flight(char *from, char *to, int seats, int price) {
    if (num_flights >= MAX_FLIGHTS) {
        printf("Sorry, the maximum number of flights has been reached.\n");
        return;
    }
    Flight new_flight;
    strcpy(new_flight.from, from);
    strcpy(new_flight.to, to);
    new_flight.seats = seats;
    new_flight.price = price;
    flights[num_flights++] = new_flight;
    printf("Flight added successfully.\n");
}

void print_flights() {
    printf("Flights:\n");
    for (int i = 0; i < num_flights; i++) {
        printf("%d. %s to %s, %d seats available, price: %d\n",
               i + 1, flights[i].from, flights[i].to, flights[i].seats, flights[i].price);
    }
}

int find_flight(char *from, char *to) {
    for (int i = 0; i < num_flights; i++) {
        if (strcmp(flights[i].from, from) == 0 && strcmp(flights[i].to, to) == 0) {
            return i;
        }
    }
    return -1;
}

void book_flight(char *from, char *to, int num_passengers) {
    int index = find_flight(from, to);
    if (index == -1) {
        printf("Sorry, no flights available from %s to %s.\n", from, to);
        return;
    }
    Flight *flight = &flights[index];
    if (flight->seats < num_passengers) {
        printf("Sorry, only %d seats available on the %s to %s flight.\n",
               flight->seats, flight->from, flight->to);
        return;
    }
    flight->seats -= num_passengers;
    printf("Successfully booked %d seats on the %s to %s flight.\n",
           num_passengers, flight->from, flight->to);
}

void cancel_flight(char *from, char *to, int num_passengers) {
    int index = find_flight(from, to);
    if (index == -1) {
        printf("Sorry, no flights available from %s to %s.\n", from, to);
        return;
    }
    Flight *flight = &flights[index];
    flight->seats += num_passengers;
    printf("Successfully cancelled %d seats on the %s to %s flight.\n",
           num_passengers, flight->from, flight->to);
}

int main() {
    add_flight("New York", "Los Angeles", 50, 500);
    add_flight("Los Angeles", "Chicago", 40, 400);
    add_flight("New York", "Chicago", 30, 450);
    print_flights();
    book_flight("New York", "Los Angeles", 2);
    book_flight("Los Angeles", "Chicago", 4);
    book_flight("New York", "Chicago", 3);
    cancel_flight("New York", "Los Angeles", 1);
    print_flights();
    return 0;
}

该代码定义了一个 `Flight` 结构体，其中包含航班的起始地点，目的地，可用座位数，价格等信息。 `add_flight` 函数用于添加新的航班， `print_flights` 函数用于打印所有可用的航班， `find_flight` 函数用于查找给定起始地点和目的地的航班， `book_flight` 函数用于预订航班， `cancel_flight` 函数用于取消预订。在 `main` 函数中，我们先添加了三个航班，然后对它们进行了一些操作，最后打印出所有可用的航班。