C语言 它在添加第一个学生的记录后停止工作，并且它不将数据保存在文件中

Question

//每当我尝试添加学生信息时，它允许我输入第一个学生的详细信息，然后在按enter键后停止工作。请帮忙，我两天后有一个报告

#include<stdio.h>
#include<ctype.h>
#include<string.h>
#include<stdlib.h>
#define NAME 50
#define LNAME 50
#define AGE 2
#define SUBJECT 200
#define ID 50

void Students();
void Subjects();

struct student{
    int ID_no;
    char name[20];
    char lname[20];
    int age[2] ;
    int id_grupi;
}; struct student stu;
struct subject
{
    char subject[20];  
    int mark[2];
};
 struct subject sub;
//initializing the files used in the program
  FILE *fp;
int main()
{
  int choice=0;
 system("cls");
           printf("ntt    ======================================");
            printf("ntt    |            Options:                |");
           printf("ntt    |                                    |");
          printf("ntt   |  [1] Add a student                 |");
           printf("ntt   |  [2] Add subject                   |");
             printf("ntt   ======================================");
            printf("n");
    scanf(" %i", &choice);
    switch (choice)
    {   
    case 1:
      Students(); 
    break;
    case 2:
      Subjects();
    default: printf("**Invalid Input.**n");
 }
 return (0);
 }
void Students() //problem when pressing enter after giving the details
{
  int select;
  char choice1;          
                            while (select!=2){
                             system("cls");
   printf("ntt              ======================================");
   printf("ntt    |                MENU:               |");
   printf("ntt    |                                    |");
   printf("ntt    |  [1] Add a student              |");
   printf("ntt    |  [2] Go back to main menu                |");
   printf("ntt    ======================================");
                             printf("ntttSelect:n ");
                                scanf("%d", &select);
                                switch(select)
                                {
    case 1: 
    system("cls");
    printf("ntttt-ADD A STUDENT-n");
    printf("NAME: ");
    scanf("%s",stu.name);
    printf("LAST NAME: ");
    scanf("%s",stu.lname);
    printf("AGE: ");
    scanf("%d",stu.age);
    printf("ID: ");
    scanf("%d",stu.ID_no); 
     fp=fopen("studentfile.txt","a+");
          fprintf(fp,"n%s    n",stu.name);
    fprintf(fp,"n%s    n",stu.lname);
    fprintf(fp,"n%d    n",stu.age);
    fprintf(fp,"n%s    n",stu.ID_no);
     fclose(fp);
                            }
                        }
  select=1;
  main();
}


void Subjects() //runs succesfully
{
  char choice2;
  int select2;
                                                                                               /* Choice2 */
                while(select2!=2){
      printf("ntt    ======================================");
      printf("ntt    |                MENU:               |");
      printf("ntt    |                                    |");
      printf("ntt    |  [1] Add subjects per student       |");
      printf("ntt    |  [2] Main menu                 |");
      printf("ntt    ======================================");
                             printf("ntttSelect: ");
                                scanf("%d", &select2);
                                switch (select2)
                                {
                                case 1:
                                        system("cls");
                                        printf("ntttt-Add subjects-");
                                        printf("nttID : ");
                                        scanf("%d", &stu.ID_no);
                          fp=fopen("studentfile.txt","a+");  
                         fprintf(fp,"n ID no:    %dn",stu.ID_no); 
                                         int i=0,l;
                                         printf("Add number of subjects: ");
                                         scanf("%d",&l);
                                         for(i=0;i<l; i++)
                                         {
                                                printf("Subject %d: ",i+1);
                                              scanf("%s",sub.subject);
                                              scanf("%s",sub.mark);

                             fprintf(fp,"Subject:   %sn",sub.subject);
                     fprintf(fp,"Mark**strong text**:    %sn",sub.nota);
                                            }

                                        fclose(fp);
                            }
                        }
  select2=1;
  main();**strong text** //runs the main function again
}`

Answer 1

使用sscanf和fgets代替scanf。像这样:

fgets(input, 50, stdin);

sscanf(input， "%d"， &choice);

将输入声明为:

字符输入[50];

每次你想从stdin或文件中读取内容时，你应该使用它，它会导致一个"强程序"。

Answer 2

除了评论中提到的未初始化变量的所有问题外，您在Modify函数中的fopen存在问题。引用文档:

"w+"  Open for reading and writing.  The file is created if it does not
      exist, otherwise it is truncated.  The stream is positioned at
      the beginning of the file.

因此，每次使用wb+打开Modify中的文件时，它都会被截断为零字节。此外，您测试fopen的方式不太好，您的错误消息也不太好。试着将其作为一般主题:

          fp = fopen("studentfile.dat", "r+b");
          if (fp == NULL)
              perror("Unable to open studentfile.dat for read and write")

可能有其他错误.....