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

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

struct Node *head = NULL;

/* Function Prototypes */
void insertEnd(int);
void insertBeginning(int);
void insertAtPosition(int, int);
void display();

/* Insert at end */
void insertEnd(int value) {
    struct Node *newNode = malloc(sizeof(struct Node));
    newNode->data = value;
    newNode->next = NULL;

    if (head == NULL) {
        head = newNode;
        return;
    }

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

    temp->next = newNode;
}

/* Insert at beginning */
void insertBeginning(int value) {
    struct Node *newNode = malloc(sizeof(struct Node));
    newNode->data = value;
    newNode->next = head;
    head = newNode;
}

/* Insert at any position */
void insertAtPosition(int value, int pos) {
    if (pos < 1) {
        printf("Invalid position\n");
        return;
    }

    if (pos == 1) {
        insertBeginning(value);
        return;
    }

    struct Node *temp = head;
    for (int i = 1; i < pos - 1 && temp != NULL; i++)
        temp = temp->next;

    if (temp == NULL) {
        printf("Invalid position\n");
        return;
    }

    struct Node *newNode = malloc(sizeof(struct Node));
    newNode->data = value;
    newNode->next = temp->next;
    temp->next = newNode;
}

/* Display list */
void display() {
    struct Node *temp = head;
    while (temp != NULL) {
        printf("%d -> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");
}

int main() {
    int choice, value, pos;

    while (1) {
        printf("\n1. Insert End\n");
        printf("2. Insert Beginning\n");
        printf("3. Insert Position\n");
        printf("4. Display\n");
        printf("0. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                printf("Enter value: ");
                scanf("%d", &value);
                insertEnd(value);
                break;
            case 2:
                printf("Enter value: ");
                scanf("%d", &value);
                insertBeginning(value);
                break;
            case 3:
                printf("Enter value: ");
                scanf("%d", &value);
                printf("Enter position: ");
                scanf("%d", &pos);
                insertAtPosition(value, pos);
                break;
            case 4:
                display();
                break;
            case 0:
                exit(0);
            default:
                printf("Invalid choice\n");
        }
    }
    return 0;
}