#include <stdio.h>
#define RECLEN 80
typedef struct noderec
          {
            char teldir[81];
            struct noderec *fw_next;
            struct noderec *bw_next;
          } node;
node *link;
node *head,*tail,*newp,*temp,*prep,*scan;
int    nc,i,loop;
char nteldir[81];
w_data(ptr)
node * ptr;
{
int j,i=0;
    if (ptr == head) j=1;
    else j=2;
    while (ptr != NULL)
          {
	     i += 1;
             printf("%4d. ",i);
             fputs(ptr->teldir,stdout);
             printf("\n");
	     if( (i % 20) == 0)
                 {
			printf("\n\n\t\t\t\t\t.... press return to continue");
			getchar();
                  }
             if (j == 1) ptr = ptr->fw_next;
             else ptr = ptr->bw_next;
          }
   if((i%20) != 0) 
      {
             printf("\n\n\t\t\t\t\t.... press return to continue");
             getchar();
      }
}
build_double_link_list()
{
int c;
     printf("\n Please keyin customer records (to exit press ^d) \n");
     while (1)
       {
         for(nc=0;(c=nteldir[nc]=getchar()) != '\n' && c != EOF; nc++);
         if (c == EOF) break;
         nteldir[nc] = '\0';
         insert();
       }
}
read_in_tel_dir()
{
int c,i=1;
FILE *fp;
     head = tail = NULL;
     fp = fopen("teldir.out","r+");
     while (1)
       {
         for(nc=0;(c=nteldir[nc]=fgetc(fp)) != '\n' && c != EOF; nc++);
         if (c == EOF) break;
         nteldir[nc] = '\0';
         newp = (node *) malloc(sizeof(node));
         if (i==1) head = newp;
         for(c=0;c<=nc;c++) newp->teldir[c] = nteldir[c];
         newp->bw_next = tail;
         if(i>1) tail->fw_next = newp;
         newp->fw_next = NULL;
         tail = newp;
         i++;
       }
     fclose(fp);
}
insert_a_record()
{
         printf("\n Please keyin the new customer record :\n");
         for(nc=0;(nteldir[nc]=getchar()) != '\n'; nc++);
         nteldir[nc] = '\0';
	 insert();
}
insert()
{
int j;
         scan = head;
         newp = (node *) malloc(sizeof(node));
         if (head == NULL) 
           {
               head = newp;
               tail = newp;
               for(j=0;j<=nc;j++) newp->teldir[j] = nteldir[j];
               return(1);
           }
         while ((j=strncmp(nteldir,scan->teldir,nc)) > 0 )
           {
           scan = scan->fw_next;
           if (scan == NULL) 
               {
                  tail->fw_next = newp;
                  newp->bw_next = tail;
                  newp->fw_next = NULL;
                  for(j=0;j<=nc;j++) newp->teldir[j] = nteldir[j];
                  tail = newp;
                  return(1);
               }
           }
         if (scan == head)
           {
                 head = newp;
                 scan->bw_next = newp;
                 for (j=0;j<=nc;j++) newp->teldir[j] = nteldir[j];
                 newp->fw_next = scan;
                 newp->bw_next = NULL;
                 return(1); 
           }
         temp = scan->bw_next;
         newp->bw_next = temp;
         newp->fw_next = scan;
         temp->fw_next = newp;
         scan->bw_next = newp;
         for(j=0; j<=nc;j++) newp->teldir[j] = nteldir[j];
  }
delete_a_record()
{
int j;
         scan = head;
         printf("\n Please keyin a customer name to be deleted \n");
         for (nc=0; (nteldir[nc]=getchar()) != '\n'; nc++);
         nteldir[nc] = '\0';
         while ( (scan != NULL) && ((j=strncmp(nteldir,scan->teldir,nc)) > 0))
               scan = scan -> fw_next;
         if (scan == NULL || j < 0) 
            {
 	     printf("\n%s not found, please check and try again\n",nteldir);
	     return(1);
            }
         if ((scan->fw_next == NULL) && (scan->bw_next == NULL)) 
            {
              printf("\nOops, you have deleted the last record in the list\n");
              head = NULL;
              tail = NULL;
              return(1);
             }
         if (scan->fw_next == NULL)
           {
              printf("\nOops, You have deleted the last record in the list\n");
              temp = scan->bw_next;
              tail = temp;
              temp->fw_next = NULL;
              return(1);
           }
         if (scan == head)
            {
              printf("\nOops, You have deleted the first record in the list\n");
              temp = scan->fw_next;
              head = temp;
              temp->bw_next = NULL;
            }
         else
            {
              temp = scan->bw_next;
              temp->fw_next = scan->fw_next;
              temp = scan->fw_next;
              temp->bw_next = scan->bw_next;
            }
} 
main()
{
  FILE *fp;
  node *ptr;
  int option=0;
   do
     {
     printf("\n\n\n\n");
     printf("\n Welcome to Telephone Directory Utility \n\n");
     printf("\n 1. Build (or append to) the double link list");
     printf("\n 2. Read in teldir.out to build the double link list");
     printf("\n 3. Insert a record");
     printf("\n 4. Delete a record");
     printf("\n 5. print out directory listing in forward order");
     printf("\n 6. Print out directory listing in backward order");
     printf("\n 7. Exit\n\n");
     printf("\n Select an option : ");
     scanf("%d",&option);
     getchar();
     if (option == 1) build_double_link_list();
     if (option == 2) read_in_tel_dir();
     if (option == 3) insert_a_record();
     if (option == 4) delete_a_record();
     if (option == 5) w_data(head);
     if (option == 6) w_data(tail);
     } while (option != 7);
     fp = fopen("teldir.out","w+");
     ptr = head;
     while(ptr != NULL)
       {
             fputs(ptr->teldir,fp);
             fputs("\n",fp);
             ptr = ptr->fw_next;
       }
     fclose(fp);
    }