#include<stdio.h>
#include<malloc.h>
#define NULL 0
#define LEN sizeof(struct student)
struct student
{
    long num;
    float score;
    struct student * next;
};
int n;
struct student * creat(void)
{
    struct student * head;
    struct student * p1, * p2;
    n = 0;
       scanf ("%ld,%f",&p1 -> num, &p1 -> score);
    head = NULL;
    while (p1 -> num != 0)
    {
        n = n + 1;
        if (n == 1)
            head = p1;
        else
            p2 -> next = p1;
        p2 = p1;
              scanf ("%ld,%f",&p1 -> num, &p1 -> score);
    }
    p2 -> next = NULL;
    return (head);
}


求教。
         p1 = p2 = (struct student *)malloc(LEN);
         p1 = (struct student *)malloc(LEN);