程序代码：

#include <stdio.h>
#include <malloc.h> 
#include <stdlib.h>
struct ListNode {
    int data;
    struct ListNode *next;
};
struct ListNode *readlist();
void printlist( struct ListNode *L )
{
     struct ListNode *p = L;
     while (p) {
           printf("%d ", p->data);
           p = p->next;
     }
     printf("\n");
}
int main()
{
    int m;
    struct ListNode *L = readlist();
    printlist(L);
    return 0;
}
struct ListNode *readlist()
{
    int a,i=0;
    struct ListNode *L,*p,*r;
    r=(struct ListNode *)malloc(sizeof(struct ListNode));
    p=r;    
    scanf("%d",&a);
    while(a!=-1)
    {        
        i++;
        if(i==1)
        {
            L=r; 
            r->data=a;
            p=r;
            r->next=NULL;
        }
        else
        {
            r->data=a;
            p->next=r;        
            p=r;
            r->next=NULL;    
        }        
        r=(struct ListNode *)malloc(sizeof(struct ListNode));
        scanf("%d",&a);
    }
    //我把while里面的两行“r->next=NULL”放在这一行输出怎么会出错呢？错误是输入的数字有的但后面全是垃圾值            
    return L;    
}