#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define LEN sizeof(struct Student)
#define STU_NUM 21

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

struct Student *create(){
    srand((time(0)));
    struct Student *a , *b , *head;
    a=b=(struct Student *)malloc(LEN);
    int n=0;
    while(n<STU_NUM){
        n=n+1;
        a->num=n;
        a->score=rand()%100+1;
        if(n==1){
            head=a;
        }else{
            b->next=a;
            b=a;
        }
        a=(struct Student *)malloc(LEN);
    }
    b->next=NULL;
    return head;
}

void print_stu(struct Student *stu_p){
    while(stu_p!=NULL){
        printf("%d号：%3.1f分\n",stu_p->num,stu_p->score);
        stu_p=stu_p->next;
    }
}

struct Student *mid_p(struct Student *stu_p){
    struct Student *mid , *fast;
    mid=fast=stu_p;
    while(fast->next!=NULL){
        if(fast->next->next!=NULL){
            fast=fast->next->next;
            mid=mid->next;
        }else{
            fast=fast->next;
        }
    }
    return mid;
}

int main(){
    struct Student *stu_p , *mid;
    stu_p=create();
    print_stu(stu_p);
    mid=mid_p(stu_p);
    printf("中间结点是%d号%3.1f分\n",mid->num,mid->score);
    return 0;
}