Circular Linked List

In the last node of a list, the link field often contains a null reference, a special value used to indicate the lack of further nodes. A less common convention is to make it point to the first node of the list; in that case the list is said to be circular or circularly linked; otherwise it is said to be open or linear.

// Program of circular linked list
#include <stdio.h>
#include <malloc.h>
 
struct node
{
  int info;
  struct node *link;
}*last;
 
main()
{
  int choice,n,m,po,i;
  last=NULL;
  while(1)
  {
    printf("1.Create List\n");
    printf("2.Add at begining\n");
    printf("3.Add after \n");
    printf("4.Delete\n");
    printf("5.Display\n");
    printf("6.Quit\n");
    printf("Enter your choice : ");
    scanf("%d",&choice);
 
    switch(choice)
    {
     case 1:
      printf("How many nodes you want : ");
      scanf("%d",&n);
      for(i=0; i < n;i++)
      {
        printf("Enter the element : ");
        scanf("%d",&m);
        create_list(m);
      }
      break;
     case 2:
      printf("Enter the element : ");
      scanf("%d",&m);
      addatbeg(m);
      break;
     case 3:
      printf("Enter the element : ");
      scanf("%d",&m);
      printf("Enter the position after which this element is inserted : ");
      scanf("%d",&po);
      addafter(m,po);
      break;
     case 4:
      if(last == NULL)
      {
        printf("List underflow\n");
        continue;
      }
      printf("Enter the number for deletion : ");
      scanf("%d",&m);
      del(m);
      break;
     case 5:
      display();
      break;
     case 6:
      exit();
     default:
      printf("Wrong choice\n");
    }/*End of switch*/
  }/*End of while*/
}/*End of main()*/
 
create_list(int num)
{
  struct node *q,*tmp;
  tmp= malloc(sizeof(struct node));
  tmp->info = num;
 
  if(last == NULL)
  {
    last = tmp;
    tmp->link = last;
  }
  else
  {
    tmp->link = last->link; /*added at the end of list*/
    last->link = tmp;
    last = tmp;
  }
}/*End of create_list()*/
 
addatbeg(int num)
{
  struct node *tmp;
  tmp = malloc(sizeof(struct node));
  tmp->info = num;
  tmp->link = last->link;
  last->link = tmp;
}/*End of addatbeg()*/
 
addafter(int num,int pos)
{
 
  struct node *tmp,*q;
  int i;
  q = last->link;
  for(i=0; i < pos-1; i++)
  {
    q = q->link;
    if(q == last->link)
    {
      printf("There are less than %d elements\n",pos);
      return;
    }
  }/*End of for*/
  tmp = malloc(sizeof(struct node) );
  tmp->link = q->link;
  tmp->info = num;
  q->link = tmp;
  if(q==last)    /*Element inserted at the end*/
    last=tmp;
}/*End of addafter()*/
 
del(int num)
{
  struct node *tmp,*q;
  if( last->link == last && last->info == num)  /*Only one element*/
  {
    tmp = last;
    last = NULL;
    free(tmp);
    return;
  }
  q = last->link;
  if(q->info == num)
  {
    tmp = q;
    last->link = q->link;
    free(tmp);
    return;
  }
  while(q->link != last)
  {
    if(q->link->info == num)     /*Element deleted in between*/
    {
      tmp = q->link;
      q->link = tmp->link;
      free(tmp);
      printf("%d deleted\n",num);
      return;
    }
    q = q->link;
  }/*End of while*/
  if(q->link->info == num)    /*Last element deleted q->link=last*/
  {
    tmp = q->link;
    q->link = last->link;
    free(tmp);
    last = q;
    return;
  }
  printf("Element %d not found\n",num);
}/*End of del()*/
 
display()
{
  struct node *q;
  if(last == NULL)
  {
    printf("List is empty\n");
    return;
  }
  q = last->link;
  printf("List is :\n");
  while(q != last)
  {
    printf("%d ", q->info);
    q = q->link;
  }
  printf("%d\n",last->info);
}/*End of display()*