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

#define LEN sizeof(struct student)  // student结构的大小

struct student *creat();            //创建链表
void print(struct student *head);   //打印链表

struct student
{
      int num;
      float score;
      struct student *next;
};

int n; //全局变量，用来记录存放了多少数据。

void main()
{
      struct student *stu;

      stu = creat();
      print( stu );

      printf("\n\n");
}

struct student *creat()
{
      struct student *head;
      struct student *p1, *p2;
  
      p1 = p2 = (struct student *)malloc(LEN);  // LEN是student结构的大小

      printf("Please enter the num :");
      scanf("%d", &p1->num);
      printf("Please enter the score :");
      scanf("%f", &p1->score);

      head = NULL;     
      n = 0;   
      
      while( 0 != p1->num )
      {
            n++;
            if( 1 == n )
            {
                  head = p1;                 
            }
            else
            {
                  p2->next = p1;
            }

            p2 = p1;

            p1 = (struct student *)malloc(LEN);

            printf("\nPlease enter the num :");
            scanf("%d", &p1->num);
            printf("Please enter the score :");
            scanf("%f", &p1->score);
      }

      p2->next = NULL;

      return head;
}

void print(struct student *head)
{
      struct student *p;
      printf("\nThere are %d records!\n\n", n);

      p = head;
      if( NULL != head )
      {
            do
            {
                  printf("学号为 %d 的成绩是: %f\n", p->num, p->score);
                  p = p->next;
            }while( NULL != p );
      }
}
源代码，请问一下struct student *creat()，这里的括号是什么意思；
struct student *creat()
{
      struct student *head;
      struct student *p1, *p2;
  
      p1 = p2 = (struct student *)malloc(LEN);  // LEN是student结构的大小

      printf("Please enter the num :");
      scanf("%d", &p1->num);
      printf("Please enter the score :");
      scanf("%f", &p1->score);

      head = NULL;     
      n = 0;   
      
      while( 0 != p1->num )
      {
            n++;
            if( 1 == n )
            {
                  head = p1;                 
            }
            else
            {
                  p2->next = p1;
            }

            p2 = p1;

            p1 = (struct student *)malloc(LEN);

            printf("\nPlease enter the num :");
            scanf("%d", &p1->num);
            printf("Please enter the score :");
            scanf("%f", &p1->score);
      }

      p2->next = NULL;

      return head;
}
结构体中为什么可以添加，while( 0 != p1->num )
      {
            n++;
            if( 1 == n )
            {
                  head = p1;                 
            }
            else
            {
                  p2->next = p1;
            }

            p2 = p1;

            p1 = (struct student *)malloc(LEN);

            printf("\nPlease enter the num :");
            scanf("%d", &p1->num);
            printf("Please enter the score :");
            scanf("%f", &p1->score);
这些