Question

How to create a singly linked list in C

Answer 1

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

/* -----------------------------
   Definition of a singly linked list node
   ----------------------------- */
typedef struct Node {
    int value;          // Data stored in the node
    struct Node *next;  // Pointer to the next node
} Node;

/* -----------------------------
   Create a new node with a given value
   Returns: pointer to the new node, or NULL on failure
   ----------------------------- */
Node *node_create(int value) {
    Node *n = malloc(sizeof(*n));
    if (!n) {
        fprintf(stderr, "Memory allocation failed\n");
        return NULL;
    }
    n->value = value;
    n->next = NULL;
    
    return n;
}

/* -----------------------------
   Insert a new value at the front of the list
   head: pointer to the head pointer (so we can modify it)
   ----------------------------- */
void list_push_front(Node **head, int value) {
    Node *n = node_create(value);
    if (!n) return;

    n->next = *head;  // New node points to old head
    *head = n;        // Head now points to new node
}

/* -----------------------------
   Insert a new value at the end of the list
   ----------------------------- */
void list_push_back(Node **head, int value) {
    Node *n = node_create(value);
    if (!n) return;

    // If the list is empty, new node becomes the head
    if (*head == NULL) {
        *head = n;
        return;
    }

    // Otherwise, walk to the last node
    Node *cur = *head;
    while (cur->next != NULL)
        cur = cur->next;

    cur->next = n;  // Attach new node at the end
}

/* -----------------------------
   Print all values in the list
   ----------------------------- */
void list_print(const Node *head) {
    printf("List: ");
    for (const Node *cur = head; cur != NULL; cur = cur->next)
        printf("%d ", cur->value);
    printf("\n");
}

/* -----------------------------
   Free all nodes in the list
   ----------------------------- */
void list_free(Node *head) {
    while (head) {
        Node *next = head->next;  // Save next pointer
        free(head);               // Free current node
        head = next;              // Move to next
    }
}

/* -----------------------------
   Demonstration of list usage
   ----------------------------- */
int main(void) {
    Node *head = NULL;  // Start with an empty list

    // Insert elements
    list_push_front(&head, 3);
    list_push_front(&head, 2);
    list_push_front(&head, 1);

    list_push_back(&head, 5);
    list_push_back(&head, 4);

    // Print the list
    list_print(head);

    // Free memory
    list_free(head);

    return 0;
}


/*
run:

List: 1 2 3 5 4 

*/

 

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