Linear Linked List

#include <stdio.h>
#include <stdlib.h>

struct node
{
  int info;
  struct node *next;
};
typedef struct node *NODEPTR;
NODEPTR list;

NODEPTR getnode (void);
void insert_list ();
int delete_list ();
void traverse ();
void insafter (int);
int delafter (int);
void freenode (NODEPTR);

int
main ()
{
  int y, x;
  int choice;

  list = getnode ();

  do
    {
      printf ("\n 1. Insert a node at the beginning of the linked list");
      printf ("\n 2. Delete a node from the beginning of the node.");
      printf ("\n 3. Show the linked list");
      printf ("\n 4. Insert a node after a specified node p");
      printf ("\n 5. Delete a node after a specified node p");
      printf ("\n 6. Exit");
      printf ("\n Enter your choice: ");
      scanf ("%d", &choice);

      switch (choice)
	{
	case 1:
	  insert_list ();
	  break;
	case 2:
	  y = delete_list ();
	  printf ("\n the deleted node: %d\n", y);
	  break;
	case 3:
	  traverse ();
	  break;
	case 4:
	  printf ("\n Insert the value of the node that you want to specify");
	  fflush (stdin);
	  scanf ("%d", &x);
	  insafter (x);
	  break;
	case 5:
	  printf ("\n Insert the value of the node that you want to specify");
	  fflush (stdin);
	  scanf ("%d", &x);
	  y = delafter (x);
	  printf ("\n the deleted node: %d\n", y);
	  break;
	case 6:
	  printf("\nExited\n");
	  exit (0);
	}
    }
  while (choice != 6);
  return 0;
}

void
insert_list ()
{
  NODEPTR p;
  int x;
  p = getnode ();
  printf ("\n Enter an element: ");
  scanf ("%d", &x);
  p->info = x;
  p->next = list->next;
  list->next = p;
}

int
delete_list ()
{
  NODEPTR p;
  int x;
  p = list->next;
  if (p == NULL)
    {
      printf ("\n List is empty");
      return -1;
    }
  x = p->info;
  list->next = p->next;
  freenode (p);
  return x;
}

void
traverse ()
{
  NODEPTR p;
  p = list->next;
  while (p != NULL)
    {
      printf ("%d ==>", p->info);
      p = p->next;
    }
}

void
insafter (int x)
{
  NODEPTR p, q;
  int x1;
  p = list;
  while (p != NULL && p->info != x)
    {
      p = p->next;
    }
  if (p == NULL)
    {
      printf ("\n Node with value %d not found", x);
      return;
    }
  q = getnode ();
  printf ("\n Enter an element: ");
  scanf ("%d", &x1);
  q->info = x1;
  q->next = p->next;
  p->next = q;
}

int
delafter (int x)
{
  NODEPTR p, q;
  int x1;
  p = list;
  while (p != NULL && p->info != x)
    {
      p = p->next;
    }
  if (p == NULL || p->next == NULL)
    {
      printf ("\n Node with value %d not found or no node after it", x);
      return -1;
    }
  q = p->next;
  x1 = q->info;
  p->next = q->next;
  freenode (q);
  return x1;
}

NODEPTR
getnode (void)
{
  NODEPTR p;
  p = (NODEPTR) malloc (sizeof (struct node));
  p->next = NULL;
  return p;
}

void
freenode (NODEPTR p)
{
  free (p);
}