有没有大佬能帮我解决一下,为啥我的链表末尾插入的是一个垃圾值，不胜感激！！！

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

//定义一个链表节点
 typedef struct node
{
    int data;
    struct node * next;
} node,*pnode;

//创建一个单链表 
pnode create_list(void)
{
    int len;
    int i;
    int val;
    pnode phead = (pnode)malloc(sizeof(node));
    pnode ptail = phead;
    ptail->next = NULL;
    if(NULL == phead)
    {
        printf("内存分配失败，停止！！！\n");
        exit(-1); 
    } 
    printf("请输入你要输入的节点个数：len = \n");
    scanf("%d",&len);
    for( i= 0;i<len;i++)
    {
        printf("请输入你要输入的%d节点值\n",i+1);
        scanf("%d",&val); 
        pnode pnew = (pnode)malloc(sizeof(node));
        if(NULL == pnew)
        {
            printf("内存分配失败，停止！！！\n");
            exit(-1); 
        } 
        pnew->data = val;
        ptail->next = pnew;
        pnew->next = NULL;
        ptail = pnew;      
    } 
    return phead;
    
}
//显示一个链表 
void traverse_list( pnode phead)
{
    pnode p = phead->next;
    while(NULL != p)
    {
        printf("%d",p->data);
        p = p->next;
    } 
    printf("\n");
    return; 
}

//判断链表是否为空 
int is_empty(pnode phead)
{
    if(NULL == phead->next)
        return 1;
    else
        return 0;
} 


//求链表的长度 
int length_list(pnode phead)
{
    pnode p = phead->next;
    int len = 0;
    while(NULL != p)
    {
        len++;
        p = p->next;
    }
    return len;
}

//给链表添加一个节点 
bool insert_list(pnode phead,int pos,int val)
{
    int i = 0;
    pnode p = phead;
    while((NULL != p)&&(i<pos-1))
    {
        p = p->next;
        ++i;
    }    
    if((NULL == p)&&(i>pos-1))
        return false;
    pnode pnew = (pnode)malloc(sizeof(node));
    if(NULL == pnew)
    {
        printf("内存分配失败\n");
        exit(-1); 
    }       
    p->data = val;
    pnode q = p->next;
    p->next = pnew;
    pnew->next = q;
    
    return true;
     
      
}

/*int delete_list(pnode,int,int*)
{
    
}*/

//给链表排序 
void sort_list(pnode phead)
{
    int i,j,t;
    int len = length_list(phead);
    pnode p,q;
    for(i = 0,p = phead->next;i<len-1;i++,p = p->next)
    {
        for(j = i+1,q = p->next;j<len;j++,q = q->next)
        {
            if(p->data>q->data)
            {
                t = p->data;
                p->data = q->data;
                q->data = t;
            }
        }
    }
    return; 
}

int main(void) 
{
    pnode phead = NULL;
    phead = create_list();
    traverse_list(phead);
    if(is_empty(phead))
        printf("链表为空\n");
    else
        printf("链表非空\n");
    printf("链表的长度为%d\n" ,length_list(phead));
    sort_list(phead);
    traverse_list(phead);    
    insert_list(phead,4,0);
    traverse_list(phead);
    
    return 0;    
} 

insert_list 里，新值赋错地方了，修改见下：

- p->data = val;
+ pnew->data = val;
  pnode q = p->next;
  p->next = pnew;
  pnew->next = q;

这样写更简单，少一行：

pnew->data = val;
pnew->next = p->next;
p->next = pnew;

运行良好，截图：