Linked List in C

What is a Node?

A node is the basic unit of a linked list. Every node contains:

• Data (value stored)
• Pointer to the next node

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

Linked List Structure (Diagram)

HEAD → [data | next] → [data | next] → [data | next] → NULL

Each node points to the next node, forming a chain.

Why Use Linked Lists?

• No need for continuous memory
• Efficient insertion & deletion anywhere
• Dynamic size – grows with memory availability
• Useful for stacks, queues, graphs, hashing

Types of Linked Lists

• Singly Linked List – Node points to next
• Doubly Linked List – Next + Previous pointers
• Circular Linked List – Last node points to first

Basic Operations

• Create Node
• Insert Node (beginning, end, position)
• Delete Node
• Traverse List
• Search Element

Examples

Example 1 – Create a Single Node

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

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

int main() {
    struct Node *head = malloc(sizeof(struct Node));

    head->data = 10;
    head->next = NULL;

    printf("Node value: %d", head->data);

    free(head);
    return 0;
}

Example 2 – Insert at Beginning

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

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

void insertBegin(struct Node **head, int value) {
    struct Node *new = malloc(sizeof(struct Node));
    new->data = value;
    new->next = *head;
    *head = new;
}

int main() {
    struct Node *head = NULL;

    insertBegin(&head, 30);
    insertBegin(&head, 20);
    insertBegin(&head, 10);

    struct Node *temp = head;
    while(temp){
        printf("%d -> ", temp->data);
        temp = temp->next;
    }
    printf("NULL");

    return 0;
}

Example 3 – Insert at End

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

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

void insertEnd(struct Node **head, int val){
    struct Node *new = malloc(sizeof(struct Node));
    new->data = val;
    new->next = NULL;

    if(*head == NULL){
        *head = new;
        return;
    }

    struct Node *temp = *head;
    while(temp->next)
        temp = temp->next;

    temp->next = new;
}

int main(){
    struct Node *head = NULL;

    insertEnd(&head, 10);
    insertEnd(&head, 20);
    insertEnd(&head, 30);

    struct Node *temp=head;
    while(temp){
        printf("%d -> ", temp->data);
        temp=temp->next;
    }
    printf("NULL");

    return 0;
}

Example 4 – Delete First Node

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

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

void deleteFirst(struct Node **head){
    if(*head == NULL) return;

    struct Node *temp = *head;
    *head = temp->next;
    free(temp);
}

int main(){
    struct Node *head = NULL;

    insertEnd(&head,10);
    insertEnd(&head,20);
    insertEnd(&head,30);

    deleteFirst(&head);

    struct Node *temp=head;
    while(temp){
        printf("%d -> ", temp->data);
        temp=temp->next;
    }
    printf("NULL");

    return 0;
}

Example 5 – Search a Value

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

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

int search(struct Node *head, int key){
    while(head){
        if(head->data == key) return 1;
        head = head->next;
    }
    return 0;
}

int main(){
    struct Node *head=NULL;

    insertEnd(&head,5);
    insertEnd(&head,10);
    insertEnd(&head,15);

    if(search(head, 10))
        printf("Found");
    else
        printf("Not Found");

    return 0;
}