#include<stdio.h>
#include<stdlib.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_s("%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_s("%ld%f", &p1->num, &p1->score);
    }
    p2->next = NULL;
    return head;
}

int main()
{
    struct student *pt;
    pt = creat();
    printf("\nnum:%ld\nscore:%5.1f\n", pt->num, pt->score);
    return 0;
}

malloc是动态分配内存的一个函数，len的大小是sizeof(struct student)，也就是结构体的大小，意思是分配一个结构体大小的内存块，把内存块的地址赋值给p2，然后把p2赋值给p1

p2指向强制转换成 struct student* 类型 的 新开辟的内存地址

struct student *它是个结构体，为p1,p2创建类型为struct student *类型的，长度为len的动态内存