Doubly

/*  Write a Program to create doubly linklist */

void first();
void last();
void disp();
void specific();
struct doubly
{
  int info;
  struct doubly *lptr,*rptr;
}*node,*l,*r,*p;

void main()
{
  int item,choice,s1;
  clrscr();
  printf("Enter an item 99 for stop : ");
  scanf("%d",&item);
  node = (struct doubly *)malloc( sizeof(struct doubly));
  l = r = p = node;
   if(item == 99)
     r = l = '\0';

  while(item!=99)
   {
     node->info = item;

     p->rptr = node;     //This two line make left to right link
     p = p->rptr;

     node->lptr = r;    //this three line make right to left link
//      r->rptr = node;
     r = node;

     node->rptr = '\0';
     node = (struct doubly *)malloc(sizeof(struct doubly));
     scanf("%d",&item);
   }

/* The above while loop will create doubly link list whose left node adress
is stored in l and right node address is stored in r */

   l->lptr = '\0';
   disp();     //Disp function is display left and right traversal.

do
 {
  printf("\n\n1 : Insert first.\n");
  printf("2 : Insert Last.\n");
  printf("3 : Insert Specific Position\n");
  printf("4 : Exit from Program.\n");
  printf("\nEnter Your Choice : ");
  scanf("%d",&choice);
  switch(choice)
   {
    case 1:
        first();
        disp();
        break;
    case 2 :
        last();
        disp();
        break;
    case 3 :
        specific();
        disp();
        break;
    case 4 :
        exit();
    default:
       printf("\n\n\t\t######## INVALID CHOICE #########\n\n");
   }
   printf("\n\nDo you want to continue? if yes, press 1 :  ");
   scanf("%d",&s1);
 }while(s1==1);
}




void disp()
{

   p = l;
   printf("\nLeft Traversal  : ");
   while(p!='\0')
    {
     printf("%d ",p->info);
     p = p->rptr;
    }

   p = r;
   printf("\nRight Traversal : ");
   while(p!='\0')
    {
     printf("%d ",p->info);
     p = p->lptr;
    }

}

void first()
{
  int item;
  printf("Enter an integer value : ");
  scanf("%d",&item);
  node = (struct doubly *)malloc( sizeof(struct doubly));
  node->lptr = '\0';
  node->info = item;


  node->rptr = l;
  l->lptr = node;
  l=node;
  if(r == '\0')
  r = l;

}
void last()
{
 int item;
  printf("Enter an integer value : ");
  scanf("%d",&item);
  node = (struct doubly *)malloc( sizeof(struct doubly));
  node->rptr = '\0';
  node->info = item;

  node->lptr = r;
  r->rptr = node;
  r=node;
  if(l=='\0')
   l = r;


}


void specific()
 {
  int item,z,n=2;
  printf("Enter an integer value : ");
  scanf("%d",&item);
  printf("Enter Position : ");
  scanf("%d",&z);
  node = (struct doubly *)malloc( sizeof(struct doubly));
  node->info = item;
  p = l;

  if(z==1)
   {
     node->lptr = '\0';
     node->rptr = l;
     l->lptr = node;
     l=node;
     if(r=='\0')
     r = l;
   }
 else
  {
    while(z>n)
     {
       p = p->rptr;
       if(p == '\0')
        {
               printf("\n\n\t\tPosition is Not Found\n");
               return;
         }
       z--;
      }
      if(p->rptr=='\0')
       {
         node->rptr = '\0';
         p->rptr = node;
         node->lptr = p;
         p = node;
         r = p;
       }

      else
       {
       p->rptr->lptr = node;
       node->rptr =  p->rptr;
       p->rptr = node;
       node->lptr = p;
      }
    }
}