To know the Doubly Linked List in C, first we should know about how the Linked List works.

Linked List

The Linked list is the linear data structure. In the Linked List the elements are stored in the nodes. The Nodes consists of Data part and Address of the next node.

In the above diagram shows the representation of the Single Linked list, every node consists of data and address of the next node. The first node in Linked list is referred as the “Head” and Last node is referred as “Tail”. The execution of the Linked List is done by pointers. In Single Linked List, the traversing is done only in forward Direction.

Difference Between Array and Linked List

Array:

In the array, the size of the array should be declared at first so, the array can’t deal with the dynamic programs which are needed to increase or decrease the size according to the problem and inserting the new elements at a position disturbs the locations of other elements. i.e., The Array is used in the static programming.

Linked List:

In the Linked List, the size of the linked list is not declared initially, we can be able to add/ delete elements according to problem. The Insertion of the elements doesn’t disturb the elements location as it is stores as dynamically and linked together with using pointers.

Syntax for declaring a Linked List.

The implementation of Linked list in C programming languages is done by the Structures and Pointers.

struct node
{
int data;
struct *next;
};

In the above code, we have declared a nose using structure and a variable for data and Pointer variable next to store the address of the next Node.

Types of Linked List:

Four types of Linked Lists are:

Single Linked List.
Doubly Linked List.
Circular single Linked List.
Circular Doubly Linked List.

Doubly Linked List:

It contains three parts. The first part is the address of previous node, data part and address of next node.

In the above diagram shows the representation of the Doubly Linked List. The “previous” part in a node contains the address of the previous node. The “next” part contains the address of the next node.

In the doubly linked list, the traversing can be done by both ways i.e., Forward and Backward.

Syntax

Syntax for declaring a double Linked List:

struct node
{
	struct node *prev;
int data;
struct node *next;
};

In the above code, a node is created using structures and a pointer variables prev and next, and an integer variable data.

The previous part value of the Head Node and Next part value of Tail node is NULL. Because the head is a first node it doesn’t contains any previous nodes so the previous is NULL, and the Tail node is the last node and it doesn’t contains any further nodes so , the next is NULL.

Program (for Doubly Linked List):

// using menu-driven method.
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
struct Node
{
struct Node *prev;
int data;
struct Node *next;
};
struct Node *head = NULL, *tail = NULL, *temp;
void insertionAtLast(int ele);
void deletionAtLast(void);
void insertionAtFirst(int ele);
void deletionAtFirst(void);
void insertionAtPosition(int ele, int pos);
void deletionAtPosition(int pos);
void traverse(void);
void insertionAtLast(int ele)
{
temp = (struct Node *)malloc(sizeof(struct Node));
temp->prev = NULL;
temp->data = ele;
temp->next = NULL;
if(head == NULL) // When list is not having any nodes.
{
head = tail = temp;
}//if
else // When list is having atleast one node.
{
tail->next = temp;
temp->prev = tail;
tail = temp;
}//else
}//insertionAtLast
void deletionAtLast(void)
{
if(head == NULL) // When list is empty.
{
printf("\nThe list is empty");
}//if
else if(head == tail) // When list is Having only one node.
{
head = tail = NULL;
}//else if
else // When list is having more than one node.
{
temp = tail;
tail = tail->prev;
tail->next = NULL;
free(temp);
}//else
}//deletionAtLast
void insertionAtFirst(int ele)
{
temp = (struct Node *)malloc(sizeof(struct Node));
temp->data = ele;
temp->next = NULL;
if(head == NULL) // When list is not having any nodes.
{
head = tail = temp;
}//if
else // When list is having atleast one node.
{
temp->next = head;
head->prev = temp;
head = temp;
}//else
}//insertionAtFirst
void deletionAtFirst(void)
{
if(head == NULL) // When list is empty.
{
printf("\nThe list is empty");
}//if
else if(head == tail) // When list is Having only one node.
{
head = tail = NULL;
}//else if
else // When list is having more than one node.
{
temp = head; // Assiging first node to temp.
head = head->next;
head->prev = NULL;
free(temp); // Deleting first node from memory.
}//else
}//deletionAtFirst
void insertionAtPosition(int ele, int pos)
{
struct Node *curr;
int i;
if(pos == 1)
{
insertionAtFirst(ele);
}//if
else
{
temp = (struct Node *)malloc(sizeof(struct Node));
temp->data = ele;
temp->next = NULL;
curr = head;
for(i=1; i<pos-1; i++) // Moving to previous of target position
{
curr = curr->next;
}//for
if(curr == NULL)
{
printf("\n Insertion not possible, Position out of range ");
}//if
else
{
temp->next = curr->next;
curr->next->prev = temp;
curr->next = temp;
temp->prev = curr;
if(curr == tail)
{
tail = temp;
}//if
}//else
}//else
}//insertionAtPosition
void deletionAtPosition(int pos)
{
int i;
if(head == NULL)
{
printf("\nList is empty");
}//if
else if(pos == 1)
{
deletionAtFirst();
}//else if
else
{
temp = head;
for(i=1; i<pos-1; i++) // Moving to previous of target position
{
temp = temp ->next;
}//for
if(temp == NULL)
{
printf("\n Deletion not possible, Position out of range");
}//if
else
{
if(temp->next == tail)
{
tail = temp;
tail->next = NULL;
}//if
else
{
temp->next = temp->next->next;
temp->next->prev = temp;
}//else
}//else
}//else
}//deletionAtPosition
void traverse(void)
{
if(head == NULL)
{
printf("\nList is empty");
}//if
else
{
temp = head;
while(temp != tail) // Diplaying all nodes except last one.
{
printf("%d <-> ", temp->data);
temp = temp -> next;
}//while
printf("%d ", temp->data);
}//else
}//traverse
void main(void)
{
int choice, ele, pos, key ;
clrscr();
while(1)
{
printf("\n \t Doubly Linked List Operations\n");
printf("1. Insert Last \n");
printf("2. Delete Last \n");
printf("3. Insert First \n");
printf("4. Delete First \n");
printf("5. Insert At Position \n");
printf("6. Delete At Position \n");
printf("7. Traverse the DLList \n");
printf("8. Exit\n");
printf("\nEnter your choice:");
scanf("%d", &choice );
switch ( choice )
{
case 1 :
printf("\nEnter the element:");
scanf("%d",&ele);
insertionAtLast(ele);
break;
case 2 :
deletionAtLast();
break;
case 3 :
printf("\nEnter the element:");
scanf("%d",&ele);
insertionAtFirst(ele);
break;
case 4 :
deletionAtFirst();
break;
case 5 :
printf("\nEnter the element:");
scanf("%d",&ele);
printf("\nEnter the position:");
scanf("%d",&pos);
insertionAtPosition(ele,pos);
break;
case 6 :
printf("\nEnter the position:");
scanf("%d",&pos);
deletionAtPosition(pos);
break;
case 7 :
traverse();
break;
case 8 :
exit(0);
default :
printf("\ninvalid choice!!!! try again!!!!\n");
break;
}//switch
}//while
}//main

Output:

Doubly Linked List Operations
1.Insert Last
2.Delete Last
3.Insert First
4.Delete First
5.Insert At Position
6.Delete At Position
7.Traverse the DLList
8.Exit
Enter your choice : 1
Enter the element:10
Doubly Linked List Operations
1.Insert Last
2.Delete Last
3.Insert First
4.Delete First
5.Insert At Position
6.Delete At Position
7.Traverse the DLList
8.Exit
Enter your choice : 8

Summary:

The doubly linked list contains previous address, next address, and data. The doubly linked list is used in the implementation of tree data structure. It is also used in undo and redo operations.

C Tutorial