C program to insert a node at any position using double linked list

A doubly linked list is a linear data structure where each node contains data and two pointers − one pointing to the previous node and another to the next node. This allows traversal in both directions and efficient insertion/deletion operations at any position.

Syntax

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

void insertAtPosition(int data, int position);

Doubly Linked List Structure

The doubly linked list structure consists of nodes where each node has three components −

• Data − stores the actual value
• Previous pointer − points to the previous node
• Next pointer − points to the next node

Example: Insert Node at Any Position

The following program demonstrates how to insert a node at any specified position in a doubly linked list −

#include <stdio.h>
#include <stdlib.h>

struct node {
    int data;
    struct node *prev;
    struct node *next;
} *head = NULL;

void createList(int n) {
    struct node *newNode, *temp;
    int data;
    
    for(int i = 0; i < n; i++) {
        printf("Enter data for node %d: ", i + 1);
        scanf("%d", &data);
        
        newNode = (struct node*)malloc(sizeof(struct node));
        newNode->data = data;
        newNode->next = NULL;
        newNode->prev = NULL;
        
        if(head == NULL) {
            head = newNode;
        } else {
            temp = head;
            while(temp->next != NULL) {
                temp = temp->next;
            }
            temp->next = newNode;
            newNode->prev = temp;
        }
    }
}

void insertAtPosition(int data, int position) {
    struct node *newNode, *temp;
    int count = 1;
    
    newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    
    if(position == 1) {
        newNode->next = head;
        newNode->prev = NULL;
        if(head != NULL) {
            head->prev = newNode;
        }
        head = newNode;
        return;
    }
    
    temp = head;
    while(temp != NULL && count < position - 1) {
        temp = temp->next;
        count++;
    }
    
    if(temp == NULL) {
        printf("Invalid position<br>");
        free(newNode);
        return;
    }
    
    newNode->next = temp->next;
    newNode->prev = temp;
    
    if(temp->next != NULL) {
        temp->next->prev = newNode;
    }
    temp->next = newNode;
}

void displayList() {
    struct node *temp = head;
    int count = 1;
    
    printf("\nDoubly Linked List: ");
    while(temp != NULL) {
        printf("Node %d: %d  ", count++, temp->data);
        temp = temp->next;
    }
    printf("<br>");
}

int main() {
    int n, data, position;
    
    printf("Enter number of nodes: ");
    scanf("%d", &n);
    
    createList(n);
    printf("\nOriginal list:");
    displayList();
    
    printf("\nEnter position to insert new node: ");
    scanf("%d", &position);
    printf("Enter data for new node: ");
    scanf("%d", &data);
    
    insertAtPosition(data, position);
    printf("\nAfter insertion:");
    displayList();
    
    return 0;
}

Enter number of nodes: 3
Enter data for node 1: 10
Enter data for node 2: 20
Enter data for node 3: 30

Original list:
Doubly Linked List: Node 1: 10  Node 2: 20  Node 3: 30  

Enter position to insert new node: 2
Enter data for new node: 15

After insertion:
Doubly Linked List: Node 1: 10  Node 2: 15  Node 3: 20  Node 4: 30  

Key Points

• Position-based insertion requires traversing to the correct position
• Memory allocation check is essential to avoid runtime errors
• Pointer updates must maintain both forward and backward links
• Edge cases include insertion at beginning, end, and invalid positions

Conclusion

Inserting a node at any position in a doubly linked list involves careful pointer manipulation to maintain both forward and backward links. The operation has O(n) time complexity for position-based access but provides flexibility for dynamic data management.