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#include <stdlib.h>
typedef struct dnode {
 int data;
 struct dnode *next, *prev;
} DNODE;

DNODE *InsFront(DNODE *, int);
DNODE *InsBefore(DNODE *, int, int);
DNODE *DelNode(DNODE *, int);
void Display(DNODE *);

main() {
 DNODE *start = NULL; /* Main Program */
 int opn, elem, info, n, i;
 do {
  clrscr();
  printf("n ### Doubly Linked List Operations ### nn");
  printf("n Press 1-Creation with front Insertion");
  printf("n       2-Insert Before a Given Node");
  printf("n       3-Delete a Given Node");
  printf("n       4-Display");
  printf("n       5-Exitn");
  printf("n       Your option ? ");
  scanf("%d", &opn);
  switch (opn) {
  case 1:
   printf("nnHow Many Nodes ?");
   scanf("%d", &n);
   for (i = 1; i <= n; i++) {
    printf("nRead the Data for Node %d ?", i);
    scanf("%d", &elem);
    start = InsFront(start, elem);
   }
   printf("nDoubly Linked list with %d nodes is ready toUse!!n", n);
   break;
  case 3:
   printf(" Read the Info of the Node to be deleted ? ");
   scanf("%d", &info);
   start = DelNode(start, info);
   break;
  case 2:
   printf(" Read the Data for New noden");
   scanf("%d", &elem);
   printf(
     " Read the Info of the Node(to the left of which new node tobe inserted ? ");
   scanf("%d", &info);
   start = InsBefore(start, elem, info);
   break;
  case 4:
   printf(" Doubly Linked List is n");
   Display(start);
   break;
  case 5:
   printf("nn Terminating nn");
   break;
  default:
   printf("nnInvalid Option !!! Try Again !! nn");
   break;
  }
  printf("nnnn  Press a Key to Continue . . . ");
  getch();
 } while (opn != 5);
}

DNODE *InsFront(DNODE *start, int elem) {
 DNODE *temp;
 temp = (DNODE *) malloc(sizeof(DNODE));
 if (temp == NULL) {
  printf(" Out of Memory !! Overflow !!!");
  return (start);
 } else {
  temp->data = elem;
  temp->prev = NULL;
  temp->next = start;
  start->prev = temp;
  printf(" New Node has been inserted at Front Successfully !!");
  return (temp);
 }
}

DNODE *InsBefore(DNODE *start, int elem, int info) {
 DNODE *temp, *t;
 temp = (DNODE *) malloc(sizeof(DNODE));
 if (temp == NULL) {
  printf(" Out of Memory !! Overflow !!!");
  return (start);
 } else {
  temp->data = elem;
  temp->next = NULL;
  temp->prev = NULL;

  if (start->data == info) /* Front Insertion */
  {
   temp->next = start;
   start->prev = temp;
   return (temp);
  } else {
   t = start;
   while (t != NULL && t->data != info)
    t = t->next;
   if (t->data == info) /* Node found */
   {
    temp->next = t;
    temp->prev = t->prev;
    t->prev->next = temp;
    t->prev = temp;
   } else
    printf(" Node not found,Invalid Info !!!");
   return (start);
  }
 }
}

DNODE *DelNode(DNODE *start, int info) {
 DNODE *t;
 if (start == NULL) {
  printf(" Underflow!!!");
  return (start);
 } else {
  t = start;
  if (start->data == info) /* Front Deletion */
  {
   start = start->next;
   start->prev = NULL;
   t->next = NULL;
   free(t);
   return (start);
  } else {
   while (t != NULL && t->data != info)
    t = t->next;
   if (t->data == info) /* node to be deleted  found*/
   {
    t->prev->next = t->next;
    t->next->prev = t->prev;
    t->next = t->prev = NULL;
    free(t);
   } else
    printf("Node not found, Invalid Info !!");
   return (start);
  }
 }
}

void Display(DNODE *start) {
 DNODE *t;
 if (start == NULL)
  printf("Empty Listn");
 else {
  t = start;
  printf("Forward Traversal nn Start->");
  while (t) {
   printf("[%d]->", t->data);
   t = t->next;
  }
  printf("Nulln");
 }
}

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