DATA STRUCTURES PROGRAM • DOUBLY & CIRCULAR LINKED LISTS

Insert at the Beginning of a Circular Linked List

Learn how to insert at the beginning of a circular linked list using a clear C program.

IntermediateCircular linked listTail pointerdo-while

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

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

void cappend(struct CNode **tail, int value)
{
    struct CNode *node = new_cnode(value);
    if (*tail == NULL) { *tail = node; return; }
    node->next = (*tail)->next;
    (*tail)->next = node;
    *tail = node;
}

void cprint(const struct CNode *tail)
{
    if (tail == NULL) { putchar('\n'); return; }
    const struct CNode *current = tail->next;
    do { printf("%d ", current->data); current = current->next; } while (current != tail->next);
    putchar('\n');
}

void cfree(struct CNode *tail)
{
    if (tail == NULL) return;
    struct CNode *head = tail->next;
    tail->next = NULL;
    while (head != NULL) { struct CNode *next = head->next; free(head); head = next; }
}

int main(void)
{
    struct CNode *tail = NULL;
    cappend(&tail, 20); cappend(&tail, 30);
    struct CNode *node = new_cnode(10);
    node->next = tail->next;
    tail->next = node;
    cprint(tail);
    cfree(tail);
    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.
Insert between the tail and current head without changing the tail pointer.
Display the computed result.

Insert between the tail and current head without changing the tail pointer.

EFFICIENCY

Time and space complexity

Time complexity

O(1)

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.