#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct names {
  char name[30];
  struct names *next;  /* pointer to next entry */
  struct names *prior;  /* pointer to previous record */
};
 
struct names *start;  /* pointer to first entry in list */
struct names *last;  /* pointer to last entry */
struct names *find(char *);
 
void enter(void);
void load(void), list(void);
void insertend(void), void modify(void);
void dls_store(struct names *i, struct names **start,
               struct names **last);
void inputs(char *, char *, int), display(struct names *);
int menu_select(void);
 
int main(void)
{
  start = last = NULL;  /* initialize start and end pointers */
 
  for(;;) {
    switch(menu_select()) {
      case 1: enter(); /* enter a name */
        break;
		case 2: insertend(); /* add a name to the list*/
        break;
		case 3: modify(); /* modify a name on the list*/
        break;
		case 5: list(); /* display the list */
        break;
      case 6: load();  /* read from disk */
        break;
      case 7: exit(0);
    }
  }
  return 0;
}
 
/* Select an operation. */
int menu_select(void)
{
  char s[80];
  int c;
 
  printf("1. Create a list of names\n");
  printf("2. Insert a name into the list.\n");
  printf("3. Modify a name on list.\n");
  printf("4. Delete a name from list.\n");
  printf("5. Display the list\n");
  printf("6. Load the file\n");
  printf("6. Quit\n");
  do {
    printf("\nEnter your choice: ");
    gets(s);
    c = atoi(s);
  } while(c<0 || c>7);
  return c;
}
 
/* Enter names. */
void enter(void)
{
  struct names *info;
 
  for(;;) {
    info = (struct names *)malloc(sizeof(struct names));
    if(!info) {
      printf("\nout of memory");
      return;
    }
 
    inputs("Enter name: ", info->name, 30);
    if(!info->name[0]) break;  /* stop entering */
 
    dls_store(info, &start, &last);
  } /* entry loop */
}
 
/* This function will input a string up to
   the length in count and will prevent
   the string from being overrun.  It will also
   display a prompting message. */
void inputs(char *prompt, char *s, int count)
{
  char p[255];
 
  do {
    printf(prompt);
    fgets(p, 254, stdin);
    if(strlen(p) > count) printf("\nToo Long\n");
  } while(strlen(p) > count);
 
  p[strlen(p)-1] = 0; /* remove newline character */
  strcpy(s, p);
}
 
/* Create a doubly linked list in sorted order. */
void dls_store(
  struct names *i,   /* new element */
  struct names **start, /* first element in list */
  struct names **last /* last element in list */
)
{
  struct names *old, *p;
 
  if(*last==NULL) {  /* first element in list */
    i->next = NULL;
    i->prior = NULL;
    *last = i;
    *start = i;
    return;
  }
  p = *start; /* start at top of list */
 
  old = NULL;
  while(p) {
    if(strcmp(p->name, i->name)<0){
      old = p;
      p = p->next;
    }
    else {
      if(p->prior) {
        p->prior->next = i;
        i->next = p;
        i->prior = p->prior;
        p->prior = i;
        return;
      }
      i->next = p; /* new first element */
      i->prior = NULL;
      p->prior = i;
      *start = i;
      return;
    }
  }
  old->next = i; /* put on end */
  i->next = NULL;
  i->prior = old;
  *last = i;
}
 
/* Remove an element from the list. */
void mldelete(struct names **start, struct names **last)
{
  struct names *info;
  char s[80];
 
  inputs("Enter name: ", s, 30);
  info = find(s);
  if(info) {
    if(*start==info) {
      *start=info->next;
      if(*start) (*start)->prior = NULL;
      else *last = NULL;
    }
    else {
      info->prior->next = info->next;
      if(info!=*last)
          info->next->prior = info->prior;
      else
        *last = info->prior;
    }
    free(info);  /* return memory to system */
  }
}
 
/* Find a name. */
struct names *find( char *name)
{
  struct names *info;
 
  info = start;
  while(info) {
    if(!strcmp(name, info->name)) return info;
    info = info->next;  /* get next name */
  }
  printf("Name not found.\n");
  return NULL;  /* not found */
}
 
/* Display the entire list. */
void list(void)
{
  struct names *info;
 
  info = start;
  while(info) {
    display(info);
    info = info->next;  /* get next name*/
  }
  printf("\n\n");
}
 
/* This function prints the fields. */
void display(struct names *info)
{
    printf("%s\n", info->name);
    printf("\n\n");
}
 
/* Load the file. */
void load()
{
  struct names *info;
  FILE *fp;
 
  fp = fopen("mlist", "rb");
  if(!fp) {
    printf("Cannot open file.\n");
    exit(1);
  }
 
  /* free any previously allocated memory */
  while(start) {
    info = start->next;
    free(info);
    start = info;
  }
 
  /* reset top and bottom pointers */
  start = last = NULL;
 
  printf("\nLoading File\n");
  while(!feof(fp)) {
    info = (struct names *) malloc(sizeof(struct names));
    if(!info) {
      printf("Out of Memory");
      return;
    }
    if(1 != fread(info, sizeof(struct names), 1, fp)) break;
    dls_store(info, &start, &last);
  }
  fclose(fp);
}