C语言如何建立动态链表问题

#include <stdio.h>
#include <stdib.h。
#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;
       p1 = p2 = (struct Student *)malloc(LEN);
       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;
             p1 = (struct Student *)malloc(LEN);
             scanf("%ld,%f,&p1->num,&p1->score);
       }
       p2->next = null;
       return (head);
}

struct node
{
　　char ch;
    int num;
　　struct node *p;
};
 
struct node a;	//声明一个结构体变量

 
#include <stdio.h>
 

struct node
{
    int num;
    struct node *next;
};
 
int main()
{
    struct node stu[3];
    struct node *head, *p;
 
    stu[0].num = 10;		//对结点的num成员赋值
    stu[1].num = 20;
    stu[2].num = 30;
 
    head = &stu[0];		//头指针指向第1个结点stu[0]
    stu[0].next = &stu[1];	//将结点stu[1]的地址赋值给stu[0]结点的next成员
    stu[1].next = &stu[2];	//将结点stu[2]的地址赋值给stu[1]结点的next成员
    stu[2].next = NULL;		//stu[2]是最后一个结点，其next成员不存放任何结点的地址，置为NULL
 
    //遍历静态链表
    p = head;			//使p指针也指向第1个结点
    
    do{
        printf("%d\n", p->num);	//输出p所指向结点的数据
        p = p->next;		//然后让p指向下一个结点
    } while (p != NULL);	//直到p的next成员为NULL，即完成遍历
 
    return 0;
}

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

struct Student
{
    int No;		//学号
    struct Student *next;
};
 
int main()
{
    struct Student *p1, *p2;
	struct Student *head, *p;
 
    int n = 0; //结点个数
 
    head = NULL;
    p1 = (struct Student *)malloc(sizeof(struct Student));
    printf("请输入第1个学号\n");
    scanf("%d", &p1->No);
 
    p2 = p1; //开始时，p1和p2均指向第1个结点
    while (p1->No != 0)
    {
        n++;
        if (n == 1)
        {
            head = p1;
        }
        else
        {
            p2->next = p1;
        }
 
        p2 = p1;//p2是最后一个结点
        printf("请输入学号，输入0终止：\n");
        p1 = (struct Student *)malloc(sizeof(struct Student));
        scanf("%d", &p1->No);
    };
 
    p2->next = NULL;//输入完毕后，p2->next为NULL
 
    //遍历动态链表
	p = head;
    printf("\n学号为：\n");
 
    while (p != NULL)
    {
        printf("%d\n", p->No);
        p = p->next;
    }
 
    return 0;
}