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C Program To Implement Doubly Linked List.

Doubly-linked list is a more sophisticated form of linked list data structure. Each node contains two fields, called links that are references to the previous and to the next node in the sequence of nodes. The two node links allow traversal of the list in either direction. The previous link of the first node and the next link of the last node points to NULL.

While adding or removing a node in a doubly linked list requires changing more links than the same operations on a singly linked list, the operations are simpler and potentially more efficient (for nodes other than first nodes) because there is no need to keep track of the previous node during traversal or no need to traverse the list to find the previous node, so that its link can be modified.

Example: A doubly linked list whose nodes contain three fields of integer value, the link to the next node, and the link to the previous node.

doubly linked list operation

Source code of Doubly Linked List:
#include <stdio.h>
#include <stdlib.h>

struct node {
struct node *prev;

int n;
struct node *next;
}*h,*temp,*temp1,*temp2,*temp4;

void insert1();
void insert2();
void insert3();
void delete1();
void traversebeg();
void traverseend(int);
void sort();
void search();
void update();
int count = 0;

main(void) {
int ch;
h = NULL;
temp = temp1 = NULL;

printf("\n 1 - Insert At Beginning");
printf("\n 2 - Insert At End");
printf("\n 3 - Insert At Any Position");
printf("\n 4 - Delete From Any Position");
printf("\n 5 - Display The List");
printf("\n 6 - Reverse The List");
printf("\n 7 - Search For Element");
printf("\n 8 - Sort The List");
printf("\n 9 - Update The List");
printf("\n 10 - Exit");

while (1) {
printf("\n\n Enter Your Choice : ");
scanf("%d", &ch);

switch (ch) {
case 1: insert1(); break;
case 2: insert2(); break;
case 3: insert3(); break;
case 4: delete1(); break;
case 5: traversebeg(); break;

case 6: temp2 = h;
if (temp2 == NULL)
printf("\n Error : List Empty To display.\n");

else {
printf("\n Reverse Order Of Linked List Is : ");
traverseend(temp2->n);
printf("\n"); }
break;

case 7: search(); break;
case 8: sort(); break;
case 9: update(); break;
case 10: exit(0);

default: printf("\n Error : Wrong Menu Choice!\n");
}}}

/* To create an empty node */
void create()
{
int data;
temp =(struct node *)malloc(1*sizeof(struct node));
temp->prev = NULL;
temp->next = NULL;

printf("\n Enter A Value To List : ");
scanf("%d", &data);
temp->n = data;
count++;
}

/*  To insert at beginning */
void insert1()
{
if (h == NULL) {
create();
h = temp;
temp1 = h;
}
else {
create();
temp->next = h;
h->prev = temp;
h = temp;
}}

/* To insert at end */
void insert2()
{
if (h == NULL) {
create();
h = temp;
temp1 = h;
}
else {
create();
temp1->next = temp;
temp->prev = temp1;
temp1 = temp;
}}

/* To insert at any position */
void insert3() {
int pos, i = 2;

printf("\n Enter Position To Be Inserted : ");
scanf("%d", &pos);
temp2 = h;

if ((pos < 1) || (pos >= count + 1)) {
printf("\n Error : Position Out Of Range To Insert.\n");
return;
}

if ((h == NULL) && (pos != 1)) {
printf("\n Error : Empty List, You Cannot Insert Other Than 1st Position.\n");
return;
}

if ((h == NULL) && (pos == 1))
{
create();
h = temp;
temp1 = h;
return;
}
else {
while (i < pos) {
temp2 = temp2->next;
i++;
}
create();
temp->prev = temp2;
temp->next = temp2->next;
temp2->next->prev = temp;
temp2->next = temp;
}}

/* To delete an element */
void delete1() {
int i = 1, pos;

printf("\n Enter Position To Be Deleted : ");
scanf("%d", &pos);
temp2 = h;

if ((pos < 1) || (pos >= count + 1)) {
printf("\n Error : Position Out Of Range To Delete.\n");
return;
}

if (h == NULL) {
printf("\n Error : Empty List! No Element To Delete.\n");
return;
}
else
{
while (i < pos) {
temp2 = temp2->next;
i++;
}
if (i == 1) {
if (temp2->next == NULL)
{
printf("\n Node Deleted From List.\n");
free(temp2);
temp2 = h = NULL;
return;
}}

if (temp2->next == NULL) {
temp2->prev->next = NULL;
free(temp2);

printf("\n Node Deleted From List.\n");
return;
}
temp2->next->prev = temp2->prev;

if (i != 1)
temp2->prev->next = temp2->next;    /* Might not need this statement if i == 1 check */

if (i == 1)
h = temp2->next;

printf("\n Node Deleted From List.\n");
free(temp2);
}
count--;
}

/* Traverse from beginning */
void traversebeg() {
temp2 = h;

if (temp2 == NULL) {
printf("\n Error : List Empty To Display.\n");
return;
}
printf("\n Linked List Elements From Begining : ");

while (temp2->next != NULL) {
printf(" %d ", temp2->n);
temp2 = temp2->next;
}
printf(" %d ", temp2->n);
printf("\n");
}

/* To traverse from end recursively */
void traverseend(int i) {
if (temp2 != NULL)
{
i = temp2->n;
temp2 = temp2->next;
traverseend(i);
printf(" %d ", i);
}}

/* To search for an element in the list */
void search() {
int data, count = 0;
temp2 = h;

if (temp2 == NULL) {
printf("\n Error : List Empty To Search For Data.\n");
return;
}
printf("\n Enter Value To Search : ");
scanf("%d", &data);

while (temp2 != NULL)
{
if (temp2->n == data) {
printf("\n Data Found In %d Position.\n",count + 1);
return;
}
else
temp2 = temp2->next;
count++;
}
printf("\n Error : %d Not found In List.\n", data);
}

/* To update a node value in the list */
void update() {
int data, data1;

printf("\n Enter The Data To Be Updated : ");
scanf("%d", &data);
printf("\n Enter New Data : ");
scanf("%d", &data1);

temp2 = h;
if (temp2 == NULL) {
printf("\n Error : List Empty, No node To Update.\n");
return;
}

while (temp2 != NULL)
{
if (temp2->n == data) {
temp2->n = data1;
traversebeg();
return;
}
else
temp2 = temp2->next;
}
printf("\n Error : %d Not Found In List To Update.\n", data);
}

/* To sort the linked list */
void sort() {
int i, j, x;
temp2 = h;
temp4 = h;

if (temp2 == NULL) {
printf("\n Error : List Empty To Sort.\n");
return;
}

for (temp2 = h; temp2 != NULL; temp2 = temp2->next) {
for (temp4 = temp2->next; temp4 != NULL; temp4 = temp4->next) {
if (temp2->n > temp4->n) {
x = temp2->n;
temp2->n = temp4->n;
temp4->n = x;
}}}
traversebeg();
}
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