1.程序功能:  数据输入输出，修改，添加，删除，并将结果保存在文件中
2.运行环境: c4droid, 苦逼手机党，，见谅
3.说明: 程序就完成了输入输出，保存，链表的建立。由于第一次独立编写，有很多不严谨的地方 ，望在测试时按数据类型与大小准确输入。电脑调试时，去掉头文件conio.h以及函数clrscr，以及更改文件路径。
3.问题: 当第一次调试时数据正确存储到文件中 但无法输出，后经调试去掉在函数data_in中的语句pfirst = NULL(这是保存头结点的变量)，去掉因为在输出函数data_out中会从新分配内存，选择先输入数据再输出之后显示成功，但数据重复显示(若有两条记录数据，会多显示两条)，若不输入数据直接显示，则数据条数正常，但多出两个零。。。。。

以下是显示情况

代码如下:
         
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>

typedef struct student
{
    int stu_id = 0;
    char name[15];
    char sex[2];
    int age = 0;
    int score = 0;
    student *next = NULL;
}stu_info;
int stu_num = 0;  //学生信息的数量
student *pfirst = NULL;  //指向链表头节点
FILE *pfile = NULL;
char fname[] = "/sdcard/stu_info.txt";

void data_in();
void data_out();
//void data_modify();
//void data_del();
void create_table(student *);
void data_save(student *);

int main(void)
{
    int fun_num = 0;  //功能序号选择
    int judge = 0;  //判断是否退出程序
   
    /*此下为主功能界面显示，可单独设置为一
    个函数*/
    puts("Please enter the function sequence"
             " number: \n");
    puts("1:The input data");
    puts("2:The output data");
    puts("3:Modify the data");
    puts("4:Delete the data");
    puts("5:Exit");
   
    while(judge != 6)
    {
        scanf("%d", &fun_num);
        switch(fun_num)
        {
            case 1:
                        data_in();
                        break;
            case 2:
                        data_out();
                        break;
        /*    case 3:
                        data_modify();
                        break;
            case 4:
                        data_del();
                        break;*/
            case 5:
                        judge = 6;
                        clrscr();
                        break;
            default:
                         puts("No found!");
                         judge = 6;
                         clrscr();
                         break;
        }
    }
    return 0;
}

void data_in()
{
    student *inf_in = NULL;  //临时存数据
    //student *data_s = NULL;  
   
    puts("Enter the number of data:");
    scanf("%d", &stu_num);
   
    for(int i = 1; i <= stu_num; i++)
    {
        inf_in = (student *)malloc(sizeof(stu_info));
        puts("Input student ID:");
        scanf("%d", &inf_in->stu_id);
        puts("Input name:");
        scanf("%s", &inf_in->name);
        puts("Input gender:");
        scanf("%s", &inf_in->sex);
        puts("Input age:");
        scanf("%d", &inf_in->age);
        puts("Input scores:");
        scanf("%d", &inf_in->score);
   
        create_table(inf_in); //实际数据至链表
    }
   
    data_save(pfirst); //存至磁盘文件
    free(inf_in);
    inf_in = NULL;
}

void create_table(student *stu_tran)
{
    static student *temp = NULL;
   
    if(!temp)
    {
        temp = stu_tran;
        pfirst = stu_tran;
    }
    else
    {
        temp->next = stu_tran;
    }
    stu_tran->next = NULL;
    temp = stu_tran;
   
}

void data_save(student *stu_tran)
{
    pfile = fopen(fname, "w");
   
    while (stu_tran)
    {
        fprintf(pfile,"%d%s%s%d%d",stu_tran->stu_id, stu_tran->name, stu_tran->sex, stu_tran->age, stu_tran->score);
        stu_tran = stu_tran->next;
    }
   
    fclose(pfile);
}

void data_out()
{
    student *stu_inf = NULL;
    puts("数据如下:");
    pfile = fopen(fname, "r");
   
   
    while(feof(pfile) == 0)
    {
        stu_inf = (student *)malloc(sizeof(stu_info));
        
        fscanf(pfile,"%d%s%s%d%d",&stu_inf->stu_id, &stu_inf->name, &stu_inf->sex, &stu_inf->age,&stu_inf->score);
        
        create_table(stu_inf);
        
    }
   
    while (pfirst)
    {
        printf("%d%s%s%d%d\n", pfirst->stu_id, pfirst->name, pfirst->sex,
        pfirst ->age, stu_inf->score);
        pfirst = pfirst -> next;
    }
   
    fclose(pfile);
    pfirst = NULL;
    free(stu_inf);
    stu_inf = NULL;
   
}

已解决，原因是链表节点分配的内存未释放。。。。。。。