29.c

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

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

struct Node* createNode(int data) {
    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
    if (newNode == NULL) {
        printf("Memory allocation failed\n");
        exit(1);
    }
    newNode->data = data;
    newNode->next = NULL;
    return newNode;
}

void insertAfter(struct Node* prevNode, int data) {
    if (prevNode == NULL) {
        printf("Previous node cannot be NULL\n");
        return;
    }

    struct Node* newNode = createNode(data);
    newNode->next = prevNode->next;
    prevNode->next = newNode;
}

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

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

    head = createNode(1);
    struct Node* second = createNode(2);
    struct Node* third = createNode(3);

    head->next = second;
    second->next = third;

    printf("Original Linked List:\n");
    printList(head);

    insertAfter(second, 4);

    printf("Linked List after insertion:\n");
    printList(head);

    free(head);
    free(second);
    free(third);

    return 0;
}