编写一个C语言程序，要求实现带头结点的链表的以下功能： 链表初始化、链表的建立（分别按头插法和尾插法两种方法建立两个链表：链表A和链表B，要求提供机会在键盘上分别依次输入两个链表的元素值）、链表A的按值查找（提供机会在键盘上输入要查找的值）、链表A的遍历、链表A的插入（提供机会在键盘上输入要插入的值和插入的位置）、链表A的删除（提供机会在键盘上输入要删除的值）、最后再把链表A和链表B进行合并，合并之后成链表C，要求链表C仍有序。（要求每一步都给出注释）

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

typedef struct ListNode {
    int data;
    struct ListNode *next;
} ListNode, *ListPtr;

// 初始化链表
void initList(ListPtr *L) {
    *L = (ListNode *) malloc(sizeof(ListNode));
    (*L)->next = NULL;
}

// 头插法建立链表
void createListHead(ListPtr L) {
    int x;
    ListNode *p;
    printf("Please input elements of the list(end with -1): ");
    scanf("%d", &x);
    while (x != -1) {
        p = (ListNode *) malloc(sizeof(ListNode));
        p->data = x;
        p->next = L->next;
        L->next = p;
        scanf("%d", &x);
    }
}

// 尾插法建立链表
void createListTail(ListPtr L) {
    int x;
    ListNode *p, *tail;
    tail = L;
    printf("Please input elements of the list(end with -1): ");
    scanf("%d", &x);
    while (x != -1) {
        p = (ListNode *) malloc(sizeof(ListNode));
        p->data = x;
        tail->next = p;
        tail = p;
        scanf("%d", &x);
    }
    tail->next = NULL;
}

// 按值查找
int findList(ListPtr L, int x) {
    ListNode *p = L->next;
    int i = 0;
    while (p) {
        i++;
        if (p->data == x) {
            printf("The index of %d in the list is %d.\n", x, i);
            return i;
        }
        p = p->next;
    }
    printf("%d is not in the list.\n", x);
    return 0;
}

// 遍历链表
void printList(ListPtr L) {
    ListNode *p = L->next;
    while (p) {
        printf("%d ", p->data);
        p = p->next;
    }
    printf("\n");
}

// 插入节点
void insertList(ListPtr L, int x, int n) {
    ListNode *p = L, *q;
    int i = 0;
    while (p && i < n - 1) {
        p = p->next;
        i++;
    }
    if (!p || i > n - 1) {
        printf("Invalid position to insert.\n");
        return;
    }
    q = (ListNode *) malloc(sizeof(ListNode));
    q->data = x;
    q->next = p->next;
    p->next = q;
    printf("Inserted %d into the list at position %d.\n", x, n);
}

// 删除节点
void deleteList(ListPtr L, int x) {
    ListNode *p = L->next, *q = L;
    while (p) {
        if (p->data == x) {
            q->next = p->next;
            free(p);
            printf("Deleted %d from the list.\n", x);
            return;
        }
        q = p;
        p = p->next;
    }
    printf("%d is not in the list.\n", x);
}

// 合并链表
void mergeList(ListPtr La, ListPtr Lb, ListPtr Lc) {
    ListNode *pa = La->next, *pb = Lb->next, *pc = Lc;
    while (pa && pb) {
        if (pa->data <= pb->data) {
            pc->next = pa;
            pa = pa->next;
        } else {
            pc->next = pb;
            pb = pb->next;
        }
        pc = pc->next;
    }
    pc->next = pa ? pa : pb;
    free(Lb);
}

int main() {
    ListPtr La, Lb, Lc;
    int x, n;
    // 初始化链表
    initList(&La);
    initList(&Lb);
    initList(&Lc);
    // 头插法建立La
    createListHead(La);
    printList(La);
    // 尾插法建立Lb
    createListTail(Lb);
    printList(Lb);
    // 查找节点
    printf("Please input the element you want to find: ");
    scanf("%d", &x);
    findList(La, x);
    // 插入节点
    printf("Please input the element and position(inserted from head) you want to insert: ");
    scanf("%d%d", &x, &n);
    insertList(La, x, n);
    printList(La);
    // 删除节点
    printf("Please input the element you want to delete: ");
    scanf("%d", &x);
    deleteList(La, x);
    printList(La);
    // 合并链表
    mergeList(La, Lb, Lc);
    printList(Lc);
    return 0;
}