2..学生信息系统DOS

/*学生信息系统DOS*/
#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>

struct student
{
 char st_name[20];
 char st_num[20];
 char st_sex;
 struct student * next;
}record;

struct student * current=NULL,* head=NULL,* build=NULL;

void main(void)
{
    int menu();
    void add();
    void del();
    void search();
    clrscr();
    while (1)
    {
        switch (menu())
     {
      case 1 : add(); continue;
      case 2 : del(); continue;
      case 3 : search(); continue;
      case 4 : printf("/n    It's wet!!!/n/n"); continue;
      case 5 : exit(0);
      default: continue;
     }
    }
    printf("/n    Thank you !!!/n/n");
}

int menu()
{
 char c[10];
 int choice;
 printf("/n    1.Add a new record");
 printf("/n    2.Delete a record");
 printf("/n    3.Search a record");
 printf("/n    4.Help");
 printf("/n    5.Quit");
 printf("/n/n    Please input:");
 gets(c);
 choice=atoi(c);
 return (choice);
}

void add()
{
 clrscr();
 if (head==NULL)
 {
  build=(struct student *)malloc(sizeof(record));
  head=build,current=build;
 }
 else
 {
  build=(struct student *)malloc(sizeof(record));
  current->next=build;
  current=build;
 }
 printf("->Input name:");
 gets(current->st_name);
 printf("->Input number:");
 gets(current->st_num);
 printf("->Input sex:");
 current->st_sex=getchar();
 current->next=NULL;
}

void del()
{
 char num[20];
 struct student *temp,*del;
 clrscr();
 printf("->Input a student's number who you want to delete it!/n");
 printf("->Input a number:");
 gets(num);
 del=head,temp=head;
 while (1)
 {
  if (!strcmp(head->st_num,num))
  {
   head=head->next;
   free(del);
   printf("->Delete Success!/n/n");
   break;
  }
  del=del->next;
  if (!strcmp(del->st_num,num))
  {
   if (del->next==NULL)
   {
    temp->next=NULL;
    free(del);
    printf("->Delete Success!/n/n");
    break;
   }
   else
   {
    temp->next=del->next;
    free(del);
    printf("->Delete Success!/n/n");
    break;
   }
  }
  else
  {
   if (del->next==NULL)
   {
    printf("->No student have been deleted, maybe you imputed a wrong number./n/n");
    break;
   }
  }
  temp=del;
 }
}

void search()
{
 char num[20];
 clrscr();
 printf("->Input a student's number who you want to find it!/n");
 printf("->Input a number:");
 gets(num);
 build=head;
 while (1)
 {
  if (!strcmp(build->st_num,num))
  {
   printf("/n%5s",build->st_name);
   printf("/n%5s",build->st_num);
   printf("/n%5c",build->st_sex);
   break;
  }
  else
  {
   if (build->next==NULL)
   {
    printf("->No student have been found./n/n");
    break;
   }
   build=build->next;
  }
 }
}