DATA STRUCTURES PROGRAM • DOUBLY & CIRCULAR LINKED LISTS

Insert at the End of a Doubly Linked List

Learn how to insert at the end of a doubly linked list using a clear C program.

IntermediateDoubly linked listpreviousnext

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

10 20 30

COMPLETE C PROGRAM

Complete C implementation

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

struct DNode { int data; struct DNode *previous; struct DNode *next; };

struct DNode *new_dnode(int value)
{
    struct DNode *node = malloc(sizeof *node);
    if (node == NULL) exit(EXIT_FAILURE);
    node->data = value; node->previous = NULL; node->next = NULL;
    return node;
}

void dappend(struct DNode **head, int value)
{
    struct DNode *node = new_dnode(value);
    if (*head == NULL) { *head = node; return; }
    struct DNode *tail = *head;
    while (tail->next != NULL) tail = tail->next;
    tail->next = node; node->previous = tail;
}

void dprint(const struct DNode *head)
{
    while (head != NULL) { printf("%d ", head->data); head = head->next; }
    putchar('\n');
}

void dfree(struct DNode *head)
{
    while (head != NULL) { struct DNode *next = head->next; free(head); head = next; }
}

int main(void)
{
    struct DNode *head = NULL;
    dappend(&head, 10); dappend(&head, 20); dappend(&head, 30);
    dprint(head);
    dfree(head);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

10 20 30

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Connect the former tail and new node through both next and previous pointers.
Display the computed result.

Connect the former tail and new node through both next and previous pointers.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.