Singly-Linked Linked List of Integers

/** NOTE: I used nothing but * notation in this program.  I expected that
you would be using pointers (->) and since the book no longer has the *
notation, I decided to give you an example.  I also added a couple of
simple functions to this program such as is_empty() which make the code a
bit more readable.  I also added several defines to enhance readability.
**/

/*****
*  Brenda Sonderegger       CS210    Fall, 1994
*
**** Linked list example ***/

#include  <stdio.h>
#include  "myio_c.h"

/**  syntatic sugar  **/

#define   TRUE    1
#define   FALSE   0
#define   INSERT  1
#define   DELETE  2
#define   PRINT   3
#define   QUIT    4

/** the structure definition and the prototypes for the functions using the
    structure all belong in a linked.h file
**/

typedef struct node_record
{
   int  info;
   struct node_record  *link;
} NODE;

/** I left variable names in to help explain what was being sent **/

int is_empty(NODE *first);
void get_memory(NODE **new_node);
void fill_node(NODE *new_node);
void insert_node(NODE **first, NODE *new_node);
/**
void create_list(NODE **first, NODE *new_node);
void add_node(NODE **first, NODE *new_node);
**/
void delete_node(NODE **first, int value);
void print_list(NODE *first);

/** print_menu() and main() should all be in a driver.c file **/
void print_menu(void);

void main(void)
{
  NODE *first, *new_node;
  int flag, option, value;

  first = new_node = NULL;
  do
  {
    print_menu();
    printf("\nEnter your choice now ");
    get_int_bound(&option, 1, 4);
    switch(option)
    {
      case INSERT: get_memory(&new_node);
                   fill_node(new_node);
                   insert_node(&first, new_node);
                   /****
                   if (is_empty(first) == TRUE)
                     create_list(&first, new_node);
                   else
                     add_node(&first, new_node);
                   ****/
                   break;
     case DELETE: if (is_empty(first) == TRUE)
                     printf("\nList is empty, cannot delete\n");
                   else
                   {
                     printf("\nEnter a value to delete ");
                     get_int(&value);
                     delete_node(&first, value);
                   }
                   break;
      case PRINT: print_list(first);
                  break;
      case QUIT: printf("\nQuitting program.\n\n");
                 break;
      default: printf("\nInvalid entry for option - try again\n");
    }
  }
  while (option != QUIT);
}



void print_menu(void)
{

   printf("\nEnter your choice \n");
   printf("\n1 - Insert a new node");
   printf("\n2 - Delete a node");
   printf("\n3 - Print the list");
   printf("\n4 - Quit the program\n");
}


/*****all functions from here down belong in linked.c file*****/
void insert_node(NODE **first, NODE *new_node)
{
  NODE *current, *previous;

  if ((*first == NULL) || ((*new_node).info <= (**first).info))
  {
    /*insert at front */
    (*new_node).link = *first;
    *first = new_node;
  }
  else
  {
    current = *first;
    while (((*new_node).info > (*current).info) && ((*current).link != NULL))
    {
      previous = current;
      current = (*current).link;
    }
    if ((*new_node).info <= (*current).info)
    {
      /* insert middle */
      (*new_node).link = current;
      (*previous).link = new_node;
    }
    else
    {
      /* insert end */
      (*current).link = new_node;
    }
  }
}



void delete_node(NODE **start, int value)
{
  NODE *current, *previous;
  int found = FALSE;

  current = *start;
  if ((*current).info == value)
  {
    found = TRUE;
    if ((*current).link == NULL)
    {
      /** only 1 element in list **/
      *start = NULL;
    }
    else
    {
      /** delete first element **/
      *start = (**start).link;
    }
  }
  else
  {
    /** delete from middle and end **/
    while (((*current).info < value) && ((*current).link != NULL))
    {
      previous = current;
      current = (*current).link;
    }
    if ((*current).info == value)
    {
      /** delete current **/
      (*previous).link = (*current).link;
      found = TRUE;
    }
  }

  if (found == TRUE)
    free((void *)current);
  else
    printf("\n%d is not in the list.\n", value);
}



void get_memory(NODE **new_node)
{
   *new_node = (NODE *)malloc(sizeof(NODE));
   if (*new_node == NULL)
   {
     printf("\n\nOut of memory - terminating.\n\n");
     exit(1);
   }
}




void fill_node(NODE *new_node)
{
  printf("\nEnter an integer ");
  get_int(&(*new_node).info);

  (*new_node).link = NULL;
}


int is_empty(NODE *first)
{
  if (first == NULL)
    return(TRUE);
  else
    return(FALSE);
}


void print_list(NODE *start)
{
  if (is_empty(start) == TRUE)
  {
    printf("\nList is empty.\n");
  }
  else
  {
    printf("\n");
    while(start != NULL)
    {
      printf("%d  ", (*start).info);
      start = (*start).link;
    }
  }
}