DATA STRUCTURES PROGRAM • SINGLY LINKED LISTS

Count Nodes in a Singly Linked List

Learn how to count nodes in a singly linked list using a clear C program.

BeginnerLinked listNodePointers

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

Nodes = 4

COMPLETE C PROGRAM

Complete C implementation

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

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

struct Node *create_node(int value)
{
    struct Node *node = malloc(sizeof *node);
    if (node == NULL) { perror("malloc"); exit(EXIT_FAILURE); }
    node->data = value;
    node->next = NULL;
    return node;
}

void append(struct Node **head, int value)
{
    struct Node *node = create_node(value);
    if (*head == NULL) { *head = node; return; }
    struct Node *current = *head;
    while (current->next != NULL) current = current->next;
    current->next = node;
}

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

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

int main(void)
{
    struct Node *head = NULL;
    append(&head, 5); append(&head, 10); append(&head, 15); append(&head, 20);
    size_t count = 0;
    for (const struct Node *current = head; current != NULL; current = current->next) count++;
    printf("Nodes = %zu\n", count);
    free_list(head);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Nodes = 4

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Increment a counter once for every node reached before NULL.
Display the computed result.

Increment a counter once for every node reached before NULL.

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.