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

/* Structure of a node */
struct node {
    int data;          // Data
    struct node *next; // Address
}*head;


int main()
{
    int n, data, position;
    //Create a singly linked list of n nodes
    printf("Enter the total number of nodes: ");
    scanf("%d", &n);
    createList(n);

    printf("\nOrginal list: \n");
    displayList();
    //Insert data between two nodes of the singly linked list
    printf("Enter data to insert a node between two nodes of the list: ");
    scanf("%d", &data);
    printf("Enter the position to insert new node: " );
    scanf("%d", &position);
    insertNodeAtbetweentwonodes(data, position);

    printf("\nUpdated list: \n");
    displayList();

    return 0;
}
//Create a list of n nodes
void createList(int n)
{
    struct node *newNode, *temp;
    int data, i;

    head = (struct node *)malloc(sizeof(struct node));
     //If unable to allocate memory for head node
    if(head == NULL)
    {
        printf("Unable to allocate memory.");
    }
    else
    {
         //Input data of node from the user
        printf("Enter the data of node 1: ");
        scanf("%d", &data);
        head->data = data; // Link the data field with data
        head->next = NULL; // Link the address field to NULL
        temp = head;
        //Creates n nodes and adds to linked list

        for(i=2; i<=n; i++)
        {
            newNode = (struct node *)malloc(sizeof(struct node));
            //If memory is not allocated for newNode
            if(newNode == NULL)
            {
                printf("Unable to allocate memory.");
                break;
            }
            else
            {
                printf("Enter the data of node %d: ", i);
                scanf("%d", &data);

                newNode->data = data; // Link the data field of newNode with data
                newNode->next = NULL; // Link the address field of newNode with NULL

                temp->next = newNode; // Link previous node i.e. temp to the newNode
                temp = temp->next;
            }
        }

        printf("LIST CREATED SUCCESSFULLY\n");
    }
}
//Creates a new node and inserts between two nodes of the linked list.
void insertNodeAtbetweentwonodes(int data, int position)
{
    int i;
    struct node *newNode, *temp;

    newNode = (struct node*)malloc(sizeof(struct node));

    if(newNode == NULL)
    {
        printf("Unable to allocate memory.");
    }
    else
    {
        newNode->data = data; // Link data part
        newNode->next = NULL;

        temp = head;
        //Traverse to the n-1 position
        for(i=2; i<=position-1; i++)
        {
            temp = temp->next;

            if(temp == NULL)
                break;
        }
        if(temp != NULL)
        {
            /* Link address part of new node */
            newNode->next = temp->next;
            /* Link address part of n-1 node */
            temp->next = newNode;
            printf("DATA INSERTED SUCCESSFULLY\n");
        }
        else
        {
            printf("UNABLE TO INSERT DATA AT THE GIVEN POSITION\n");
        }
    }
}
//Display entire list
void displayList()
{
    struct node *temp;
    //If the list is empty i.e. head = NULL
    if(head == NULL)
    {
        printf("List is empty.");
    }
    else
    {
        temp = head;
        while(temp != NULL)
        {
            printf("%d -> ", temp->data); // Print data of current node
            temp = temp->next;                 // Move to next node
        }
        printf("NULL\n");
    }
}