为什么不能运行？该如何修改？

修改如下，供参考：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct dat {
    char name[5];
    char sex[5];
    char major[20];
    char clas[5];
    char birthday[20];
    char stu_code[20];
    char id_code[20];
    char enyear[10];
}Data;
typedef struct lnode {
    Data   data;
    struct lnode* next;
}LNode;
void sort()
{
    FILE* fp;
    int  a = 0;
    char na[10], i[10], j[10];
    char clas[10], stu_code[15], id_code[20];
    char sex[5], enyear[10], birthday[20], major[20], name[10];
    LNode* tail = NULL, * head = NULL, * pMove = NULL, * n = NULL, * pNext = NULL;
    Data  temp;
    if ((fp = fopen("test.dat", "r")) == NULL)
    {
        printf("open file fail!\n");
        return;
    }
    while (1)
    {
        if (fscanf(fp, "%s %s %s %s %s %s %s %s\n", name, sex, major, clas,
                                   birthday, stu_code, id_code, enyear) != 8) break;
        n = (LNode*)malloc(sizeof(LNode));
        n->next = NULL;
        strcpy(n->data.clas, clas); strcpy(n->data.stu_code, stu_code);
        strcpy(n->data.id_code, id_code);
        strcpy(n->data.name, name); strcpy(n->data.sex, sex);
        strcpy(n->data.major, major); strcpy(n->data.enyear, enyear);
        strcpy(n->data.birthday, birthday);
        if (head == NULL)
            head = n;
        else
            tail->next = n;
        tail = n;
    }
    fclose(fp);
    while (a != 3)
    {
        printf("----------1.按班级排序-------------\n");
        printf("----------2.按学籍号码排序----------\n");
        printf("----------3.退出------------------\n");
        scanf("%d", &a);
        switch (a)
        {
        case 1: 
            pMove = head;
            while (pMove)
            {
                pNext = pMove->next;
                while (pNext != NULL)
                {
                    if (strcmp(pMove->data.clas, pNext->data.clas) > 0)
                    {
                        temp= pMove->data;
                        pMove->data = pNext->data;
                        pNext->data = temp;
                    }
                    pNext = pNext->next;
                }
                pMove = pMove->next;
            }
            break;
        case 2:
            pMove = head;
            while (pMove)
            {
                pNext = pMove->next;
                while (pNext != NULL)
                {
                    if (strcmp(pMove->data.id_code, pNext->data.id_code) > 0)
                    {
                        temp = pMove->data;
                        pMove->data = pNext->data;
                        pNext->data = temp;
                    }
                    pNext = pNext->next;
                }
                pMove = pMove->next;
            }
            break;
        case 3:printf("退出排序!\n"); return;
        default:printf("输入错误，请重新输入！\n"); break;
        }
        pMove = head;
        while (pMove != NULL)
        {
            printf("%5s%5s%20s%5s%20s%20s%20s%10s\n", pMove->data.name,
                     pMove->data.sex, pMove->data.major, pMove->data.clas,
                    pMove->data.birthday, pMove->data.stu_code,
                    pMove->data.id_code, pMove->data.enyear);
            pMove = pMove->next;
        }
    }
}