无头结点的单链表尾插法创建输不出结果

#include <stdio.h>
#include <stdlib.h>
struct ListNode 
{
    int data;
    struct ListNode *next;
};
void readlist()
{
    struct ListNode *head,*p,*q;
    int i;
    head=(struct ListNode*)malloc(sizeof(struct ListNode)); 
    head->next=NULL;
    p=head;
    while(1)
    {
        scanf("%d",&i);
        if(i==-1)
        break;
        q=(struct ListNode*)malloc(sizeof(struct ListNode));
        q->next=NULL;
        q->data=i;
        q=p;
        p=p->next;
 }
 p->next=NULL;
    
 } 
 int main ()
 {
     struct ListNode *head,*p;
     readlist();
     p=head;
     while(p)
     {
         printf("%d ",p->data);
         p=p->next;
     }
 }

 
#include <stdio.h>
#include <stdlib.h>
struct ListNode 
{
    int data;
    struct ListNode *next;
};
struct ListNode * readlist()
{
    struct ListNode *head=NULL,*p,*q;
    int i;
    while(1)
    {
        scanf("%d",&i);
        if(i==-1)
            break;
        q=(struct ListNode*)malloc(sizeof(struct ListNode));
        q->next=NULL;
        q->data=i;
        if(head == NULL)
            p = head = q;
        else 
        {
            p->next = q;
            p = p->next;
        }
 }
 p->next=NULL;
return head;
 } 
 int main ()
 {
     struct ListNode *head,*p;
     head  = readlist();
     p=head;
     while(p)
     {
         printf("%d ",p->data);
         p=p->next;
     }
     return 0;
 }

你readlist()函数应该返回head啊
你题目的解答代码如下：

#include <stdio.h>
#include <stdlib.h>
struct ListNode
{
    int data;
    struct ListNode *next;
};
struct ListNode *readlist()
{
    struct ListNode *head, *p, *q;
    int i;
    head = (struct ListNode *)malloc(sizeof(struct ListNode));
    head->next = NULL;
    p = head;
    while (1)
    {
        scanf("%d", &i);
        if (i == -1)
            break;
        q = (struct ListNode *)malloc(sizeof(struct ListNode));
        q->next = NULL;
        q->data = i;
        p->next = q;
        p = q;
    }
    p->next = NULL;
    return head;
}
int main()
{
    struct ListNode *head, *p;
    head = readlist();
    p = head->next;
    while (p)
    {
        printf("%d ", p->data);
        p = p->next;
    }
}

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