关于#链表#的问题，如何解决？

Question

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#define N 4    //课程数目 
typedef struct stu
{
    long  stuID;     //学号
    char  stuname[10]; //名字
    char  stusex;  //性别
    int   score[N]; //分数
    int   total;   //总分
    float aver;    //平均分
    int   line;    //排名
}STU;
typedef struct node //创建结点类型
{
    STU stu;        //数据域
    struct node* next;//指向下一个节点的指针
}NODE;
NODE* head = NULL; //定义头指针

void start();
void inputstudent();
void savestudent();
void readstudent();
void printfstudent(NODE* p = NULL);
void rank();//排名次函数
NODE* find_id(long id);
NODE* find_name(char*);
void swap(STU& stu1, STU& stu2);
void paixu1();
void paixu2();

int main()
{
    int exit = 0; long id; char name[10]; NODE* pt = NULL;
    while (1)
    {
        start();
        char ch = _getch();
        switch (ch)
        {
        case '1': //录入学生信息
            inputstudent();
            rank();
            break;
        case '2':  //保存学生信息
            savestudent();
            break;
        case '3'://读取学生信息
            readstudent();
            break;
        case '4':  //打印学生信息
            printfstudent();
            break;
        case'5':  //根据学号查询学生
            printf("请输入学号：");
            scanf_s("%ld", &id);
            pt = find_id(id);
            if (pt)
                printfstudent(pt);
            else
                printf("未找到该学号学生的记录!\n");
            break;
        case'6':  //根据姓名查询学生
            printf("请输入姓名：");
            scanf_s("%s", name, 10);
            pt = find_name(name);
            if (pt)
                printfstudent(pt);
            else
                printf("未找到该姓名学生的记录!\n");
            break;
        case '7':  //按学号由小到大排出成绩表
            paixu1();
            printfstudent();   //打印学生信息同时按由高到低排名
            break;
        case '8':  //按姓名字典顺序排序排出成绩表
            paixu2();
            printfstudent();
            break;
        case '0':
            printf("再见！\n");
            exit = 1;
            break;
        default:
            printf("菜单选择错误，请重新选择！\n");
            break;
        }
        if (exit)  break;
    }
    return 0;
}

void start()
{
    printf("*****************************************\n");
    printf("欢迎使用学生成绩管理系统                *\n");
    printf("*1.录入学生信息                         *\n");
    printf("*2.保存学生信息                         *\n");
    printf("*3.读取学生信息                         *\n");
    printf("*4.打印学生信息                         *\n");
    printf("*5.按学号查询学生的分数及名次           *\n");
    printf("*6.按姓名查询学生的分数及名次           *\n");
    printf("*7.按学号由小到大排出成绩表             *\n");
    printf("*8.按姓名字典顺序排序排出成绩表         *\n");
    printf("*0.退出系统！                           *\n");
    printf("*****************************************\n");
}

void inputstudent()
{
    int  i;
    NODE* newnode = (NODE*)malloc(sizeof(NODE));
    newnode->next = NULL;
    printf("学号：");
    scanf_s("%ld", &newnode->stu.stuID);
    printf("姓名：");
    scanf_s("%s", newnode->stu.stuname, 10);
    printf("性别：");
    scanf_s(" %c", &newnode->stu.stusex, 1);
    printf("%d门课程成绩：", N);
    for (i = 0, newnode->stu.total = 0; i < N; i++) { //输入4科成绩并计算总分
        scanf_s("%d", &newnode->stu.score[i]);
        newnode->stu.total += newnode->stu.score[i];
    }
    newnode->stu.aver = (float)(newnode->stu.total / N); //计算平均数
    if (head == NULL)
        head = newnode;
    else
    {
        NODE* p = head;
        while (p->next && p->next->stu.total > newnode->stu.total)
            p = p->next;
        if (p == head && p->stu.total < newnode->stu.total) {
            newnode->next = head;
            head = newnode;
        }
        else {
            newnode->next = p->next;
            p->next = newnode;
        }
    }
}

void savestudent()    //保存学生信息
{
    FILE* pf = fopen("pph.txt", "w"); //创建并打开文件
    if (pf == NULL) //判断打开文件是否失败
    {
        printf("打开文件失败\n");
        return;
    }
    NODE* p = head;
    while (p != NULL) {
        fwrite(&p->stu, sizeof(STU), 1, pf);
        p = p->next;
    }
    fclose(pf);
    printf("数据保存成功\n");
}


void readstudent()   //读取学生信息
{
    FILE* pf = fopen("pph.txt", "r");  //打开文件
    if (pf == NULL) //判断打开文件是否失败
    {
        printf("err!\n");
        return;
    }
    NODE* pt = NULL;
    while (1)
    {
        NODE* newnode = (NODE*)malloc(sizeof(NODE));
        newnode->next = NULL;
        if (fread(&newnode->stu, sizeof(STU), 1, pf) != 1) {
            free(newnode);
            break;
        }
        if (head == NULL)
            head = newnode;
        else {
            if (!pt) {
                pt = head;
                while (pt->next) pt = pt->next;
            }
            pt->next = newnode;
            pt = newnode;
        }
    }
    fclose(pf);
    printf("加载数据成功\n");
}
void printfstudent(NODE* p)
{
    int i;
    NODE* P = NULL;
    if (!p)
        P = head;
    else
        P = p;
    while (P != NULL) {
        printf("%ld %s %c", P->stu.stuID, P->stu.stuname, P->stu.stusex);
        for (i = 0; i < N; i++)
            printf(" %d", P->stu.score[i]);
        printf(" %d %.2f %d\n", P->stu.total, P->stu.aver, P->stu.line);
        if (!p)
            P = P->next;
        else
            break;
    }
    system("pause");
}

void rank()// 排名次函数
{
    int k = 0;
    NODE* P = head, * pre = NULL;
    while (P != NULL) {
        if (P == head)
            k++;
        else if (pre->stu.total != P->stu.total) {
            k++;
        }
        P->stu.line = k;
        pre = P;
        P = P->next;
    }
}

NODE* find_id(long id) //按学号查找
{
    NODE* p = head;
    while (p) {
        if (p->stu.stuID == id)
            return p;
        p = p->next;
    }
    return NULL;
}

NODE* find_name(char* name)//按姓名查找
{
    NODE* p = head;
    while (p) {
        if (strcmp(p->stu.stuname, name) == 0)
            return p;
        p = p->next;
    }
    return NULL;
}
void swap(STU& stu1, STU& stu2)
{
    STU temp;
    temp = stu1;
    stu1 = stu2;
    stu2 = temp;
}

void paixu1()
{
    NODE* p = NULL, * pre = NULL;
    if (!head)  return;
    for (p = head; p->next != NULL; p = p->next)
        for (pre = p->next; pre != NULL; pre = pre->next)
            if (p->stu.stuID > pre->stu.stuID)  //按学号从小到大排序
                swap(p->stu, pre->stu);
}

void paixu2()
{
    NODE* p = NULL, * pre = NULL;
    if (!head)  return;
    for (p = head; p->next != NULL; p = p->next)
        for (pre = p->next; pre != NULL; pre = pre->next)
            if (strcmp(p->stu.stuname, pre->stu.stuname) > 0) //按姓名字典顺序排序
                swap(p->stu, pre->stu);
}
求大佬帮忙写一下关于链表的代码的注释，最好详细一点

Answer 1

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