航班售票系统，要求完成以下功能： 1 假设该民航有若干航班，要求实现增加航班和取消某个航班的功能。 2 查询：根据用户提出的终到站查询航班号、售票情况等航班信息；也可根据 航班号，列出该航班已订票的乘客名单。 3 订票：根据航班号为客户订票，如该航班有余票，则为客户订票；如该航班 已满员，则显示相应信息。 4 退票：按乘客要求退出已预定的机票。 提示： 数据结构：可以使用链表表示航线表，对每个航班应包括以下信息：航班号、到 达港、总座位数、余票额、乘客名单等；其中乘客名单应为一个单链表，每个乘 客的信息有：乘客姓名、证件号码、座位号等，为方便查找，可考虑按乘客姓名 排序；相应数据类型示范如下： struct cnode{ char name[20]; //乘客姓名 char idcard[30]; //证件号码 int seatno; //座位号 struct cnode *clink; //下一乘客指针 }; struct pnode{ int no; //航班号 char destin[30]; //到达站 int limit,rest; //总座位数、余票额 struct cnode *clist; //乘客名单 struct pnode *plink; //下一航班指针 };请写出代码

由于这是一个完整的系统，我无法在这里直接给出完整的代码，但是我可以提供大致的思路和代码框架。

首先，我们需要定义两个结构体，分别表示乘客和航班信息：

struct Passenger {
    char name[20];
    char idcard[30];
    int seatno;
    struct Passenger *next;
};

struct Flight {
    int no;
    char destin[30];
    int limit;
    int rest;
    struct Passenger *passenger_list;
    struct Flight *next;
};

接下来，我们需要实现增加航班和取消某个航班的功能。这可以通过链表来实现。我们可以定义一个指向航班链表头的指针 flight_list，然后通过遍历链表来实现增加和取消：

struct Flight *flight_list = NULL;

// 增加航班
void add_flight(int no, char *destin, int limit) {
    struct Flight *new_flight = (struct Flight *)malloc(sizeof(struct Flight));
    new_flight->no = no;
    strcpy(new_flight->destin, destin);
    new_flight->limit = limit;
    new_flight->rest = limit;
    new_flight->passenger_list = NULL;
    new_flight->next = flight_list;
    flight_list = new_flight;
}

// 取消航班
void cancel_flight(int no) {
    struct Flight *prev = NULL;
    struct Flight *cur = flight_list;
    while (cur != NULL) {
        if (cur->no == no) {
            if (prev == NULL) {
                flight_list = cur->next;
            } else {
                prev->next = cur->next;
            }
            free(cur);
            return;
        }
        prev = cur;
        cur = cur->next;
    }
}

接下来是查询功能，根据提出的终到站查询航班号、售票情况等航班信息。我们可以遍历航班链表，找到到达港和航班号匹配的航班，然后输出相关信息。对于根据航班号列出该航班已订票的乘客名单这一功能，我们可以在找到航班后遍历该航班的乘客链表，然后输出相关信息：

// 查询航班
void query_flight(char *destin) {
    struct Flight *cur = flight_list;
    while (cur != NULL) {
        if (strcmp(cur->destin, destin) == 0) {
            printf("Flight No.: %d\n", cur->no);
            printf("Destination: %s\n", cur->destin);
            printf("Total seats: %d\n", cur->limit);
            printf("Rest seats: %d\n", cur->rest);
            printf("Passenger list:\n");
            struct Passenger *p = cur->passenger_list;
            while (p != NULL) {
                printf("%s %s %d\n", p->name, p->idcard, p->seatno);
                p = p->next;
            }
            return;
        }
        cur = cur->next;
    }
    printf("No flights to %s\n", destin);
}

// 列出乘客名单
void list_passengers(int no) {
    struct Flight *cur = flight_list;
    while (cur != NULL) {
        if (cur->no == no) {
            printf("Passenger list of flight No.%d:\n", no);
            struct Passenger *p = cur->passenger_list;
            while (p != NULL) {
                printf("%s %s %d\n", p->name, p->idcard, p->seatno);
                p = p->next;
            }
            return;
        }
        cur = cur->next;
    }
    printf("No such flight\n");
}

订票和退票的功能也可以通过遍历航班链表和乘客链表来实现。对于订票，我们需要找到航班和乘客名单，如果航班还有余票，则将该乘客加入乘客链表；对于退票，我们需要找到乘客，然后将其从乘客链表中删除：

// 订票
void book_ticket(int no, char *name, char *idcard) {
    struct Flight *cur = flight_list;
    while (cur != NULL) {
        if (cur->no == no) {
            if (cur->rest == 0) {
                printf("The flight is full\n");
                return;
            }
            struct Passenger *p = (struct Passenger *)malloc(sizeof(struct Passenger));
            strcpy(p->name, name);
            strcpy(p->idcard, idcard);
            p->seatno = cur->limit - cur->rest + 1;
            cur->rest--;
            p->next = cur->passenger_list;
            cur->passenger_list = p;
            printf("Ticket booked successfully\n");
            return;
        }
        cur = cur->next;
    }
    printf("No such flight\n");
}

// 退票
void cancel_ticket(int no, char *name) {
    struct Flight *cur = flight_list;
    while (cur != NULL) {
        struct Passenger *prev = NULL;
        struct Passenger *p = cur->passenger_list;
        while (p != NULL) {
            if (strcmp(p->name, name) == 0) {
                if (prev == NULL) {
                    cur->passenger_list = p->next;
                } else {
                    prev->next = p->next;
                }
                cur->rest++;
                free(p);
                printf("Ticket canceled successfully\n");
                return;
            }
            prev = p;
            p = p->next;
        }
        cur = cur->next;
    }
    printf("No such passenger\n");
}

最后，我们需要一个主函数来驱动整个程序，接收用户的输入并调用相应的函数：

int main() {
    while (1) {
        printf("Please select an operation:\n");
        printf("1. Add a flight\n");
        printf("2. Cancel a flight\n");
        printf("3. Query flight information\n");
        printf("4. List passengers of a flight\n");
        printf("5. Book a ticket\n");
        printf("6. Cancel a ticket\n");
        printf("7. Exit\n");
        int op;
        scanf("%d", &op);
        if (op == 1) {
            int no, limit;
            char destin[30];
            printf("Please enter the flight No.: ");
            scanf("%d", &no);
            printf("Please enter the destination: ");
            scanf("%s", destin);
            printf("Please enter the total seats: ");
            scanf("%d", &limit);
            add_flight(no, destin, limit);
            printf("Flight added successfully\n");
        } else if (op == 2) {
            int no;
            printf("Please enter the flight No.: ");
            scanf("%d", &no);
            cancel_flight(no);
            printf("Flight canceled successfully\n");
        } else if (op == 3) {
            char destin[30];
            printf("Please enter the destination: ");
            scanf("%s", destin);
            query_flight(destin);
        } else if (op == 4) {
            int no;
            printf("Please enter the flight No.: ");
            scanf("%d", &no);
            list_passengers(no);
        } else if (op == 5) {
            int no;
            char name[20], idcard[30];
            printf("Please enter the flight No.: ");
            scanf("%d", &no);
            printf("Please enter your name: ");
            scanf("%s", name);
            printf("Please enter your ID card number: ");
            scanf("%s", idcard);
            book_ticket(no, name, idcard);
        } else if (op == 6) {
            int no;
            char name[20];
            printf("Please enter the flight No.: ");
            scanf("%d", &no);
            printf("Please enter your name: ");
            scanf("%s", name);
            cancel_ticket(no, name);
        } else if (op == 7) {
            break;
        } else {
            printf("Invalid operation\n");
        }
    }
    return 0;
}

以上是一个简单的航班售票系统的代码框架，你可以根据自己的需要进行修改和完善。