用C语言编写代码实现单链表的建立、输出、插入、删除、判断链表是否为空、输出链表长度，并且当输入1时为插入操作

好，下面是用C语言实现单链表的代码：

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

//定义链表结构体
struct ListNode {
    int val;
    struct ListNode *next;
};

//创建链表
struct ListNode* createList() {
    struct ListNode *head = NULL;
    struct ListNode *tail = NULL;
    int val;
    printf("请输入链表节点的值（输入-1结束）：");
    while (1) {
        scanf("%d", &val);
        if (val == -1) {
            break;
        }
        struct ListNode *node = (struct ListNode*)malloc(sizeof(struct ListNode));
        node->val = val;
        node->next = NULL;
        if (head == NULL) {
            head = node;
            tail = node;
        } else {
            tail->next = node;
            tail = node;
        }
    }
    return head;
}

//输出链表
void printList(struct ListNode *head) {
    if (head == NULL) {
        printf("链表为空！\n");
        return;
    }
    printf("链表节点的值为：");
    while (head != NULL) {
        printf("%d ", head->val);
        head = head->next;
    }
    printf("\n");
}

//插入节点
struct ListNode* insertNode(struct ListNode *head) {
    int val, pos;
    printf("请输入要插入的节点的值和插入位置：");
    scanf("%d %d", &val, &pos);
    struct ListNode *node = (struct ListNode*)malloc(sizeof(struct ListNode));
    node->val = val;
    if (pos == 1) {
        node->next = head;
        head = node;
    } else {
        struct ListNode *pre = head;
        for (int i = 1; i < pos - 1; i++) {
            pre = pre->next;
        }
        node->next = pre->next;
        pre->next = node;
    }
    return head;
}

//删除节点
struct ListNode* deleteNode(struct ListNode *head) {
    int val;
    printf("请输入要删除的节点的值：");
    scanf("%d", &val);
    struct ListNode *pre = head;
    if (head->val == val) {
        head = head->next;
        free(pre);
    } else {
        while (pre->next != NULL && pre->next->val != val) {
            pre = pre->next;
        }
        if (pre->next == NULL) {
            printf("要删除的节点不存在！\n");
        } else {
            struct ListNode *del = pre->next;
            pre->next = del->next;
            free(del);
        }
    }
    return head;
}

//判断链表是否为空
int isEmpty(struct ListNode *head) {
    return head == NULL;
}

//输出链表长度
int length(struct ListNode *head) {
    int len = 0;
    while (head != NULL) {
        len++;
        head = head->next;
    }
    return len;
}

int main() {
    struct ListNode *head = createList();
    printList(head);
    int op;
    printf("请选择操作（1 插入节点，2 删除节点）：");
    scanf("%d", &op);
    switch (op) {
        case 1:
            head = insertNode(head);
            break;
        case 2:
            head = deleteNode(head);
            break;
        default:
            printf("无效操作！\n");
    }
    printList(head);
    printf("链表是否为空：%d\n", isEmpty(head));
    printf("链表长度为：%d\n", length(head));
    return 0;
}

以上代码实现了单链表的创建、输出、插入、删除、判断链表是否为空、输出链表长度，并且当输入1时为插入操作。