text: // A complete working C program to demonstrate all insertion methods 
  #include <stdio.h> 
  #include <stdlib.h> 
    
  // A linked list node 
  struct Node { 
      int data; 
      struct Node* next; 
      struct Node* prev; 
  }; 
    
  /* Given a reference (pointer to pointer) to the head of a list 
     and an int, inserts a new node on the front of the list. */
  void push(struct Node** head_ref, int new_data) 
  { 
      /* 1. allocate node */
      struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
    
      /* 2. put in the data  */
      new_node->data = new_data; 
    
      /* 3. Make next of new node as head and previous as NULL */
      new_node->next = (*head_ref); 
      new_node->prev = NULL; 
    
      /* 4. change prev of head node to new node */
      if ((*head_ref) != NULL) 
          (*head_ref)->prev = new_node; 
    
      /* 5. move the head to point to the new node */
      (*head_ref) = new_node; 
  } 
    
  /* Given a node as prev_node, insert a new node after the given node */
  void insertAfter(struct Node* prev_node, int new_data) 
  { 
      /*1. check if the given prev_node is NULL */
      if (prev_node == NULL) { 
          printf("the given previous node cannot be NULL"); 
          return; 
      } 
    
      /* 2. allocate new node */
      struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
    
      /* 3. put in the data  */
      new_node->data = new_data; 
    
      /* 4. Make next of new node as next of prev_node */
      new_node->next = prev_node->next; 
    
      /* 5. Make the next of prev_node as new_node */
      prev_node->next = new_node; 
    
      /* 6. Make prev_node as previous of new_node */
      new_node->prev = prev_node; 
    
      /* 7. Change previous of new_node's next node */
      if (new_node->next != NULL) 
          new_node->next->prev = new_node; 
  } 
    
  /* Given a reference (pointer to pointer) to the head 
     of a DLL and an int, appends a new node at the end  */
  void append(struct Node** head_ref, int new_data) 
  { 
      /* 1. allocate node */
      struct Node* new_node = (struct Node*)malloc(sizeof(struct Node)); 
    
      struct Node* last = *head_ref; /* used in step 5*/
    
      /* 2. put in the data  */
      new_node->data = new_data; 
    
      /* 3. This new node is going to be the last node, so 
            make next of it as NULL*/
      new_node->next = NULL; 
    
      /* 4. If the Linked List is empty, then make the new 
            node as head */
      if (*head_ref == NULL) { 
          new_node->prev = NULL; 
          *head_ref = new_node; 
          return; 
      } 
    
      /* 5. Else traverse till the last node */
      while (last->next != NULL) 
          last = last->next; 
    
      /* 6. Change the next of last node */
      last->next = new_node; 
    
      /* 7. Make last node as previous of new node */
      new_node->prev = last; 
    
      return; 
  } 
    
  // This function prints contents of linked list starting from the given node 
  void printList(struct Node* node) 
  { 
      struct Node* last; 
      printf("\nTraversal in forward direction \n"); 
      while (node != NULL) { 
          printf(" %d ", node->data); 
          last = node; 
          node = node->next; 
      } 
    
      printf("\nTraversal in reverse direction \n"); 
      while (last != NULL) { 
          printf(" %d ", last->data); 
          last = last->prev; 
      } 
  } 
    
  /* Driver program to test above functions*/
  int main() 
  { 
      /* Start with the empty list */
      struct Node* head = NULL; 
    
      // Insert 6.  So linked list becomes 6->NULL 
      append(&head, 6); 
    
      // Insert 7 at the beginning. So linked list becomes 7->6->NULL 
      push(&head, 7); 
    
      // Insert 1 at the beginning. So linked list becomes 1->7->6->NULL 
      push(&head, 1); 
    
      // Insert 4 at the end. So linked list becomes 1->7->6->4->NULL 
      append(&head, 4); 
    
      // Insert 8, after 7. So linked list becomes 1->7->8->6->4->NULL 
      insertAfter(head->next, 8); 
    
      printf("Created DLL is: "); 
      printList(head); 
    
      getchar(); 
      return 0; 
  }  