DSA_9

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
struct node
{
    int data;
    struct node *next;
    struct node *prev;

};

void linkedlist(struct node *head)
{
    struct node *ptr = head;
    while(ptr!=NULL)
    {
        printf("Element : %d\n",ptr->data);
        ptr = ptr->next;
    }
}

struct node *insertatfirst(struct node *head,int data)
{
    struct node *ptr = (struct node *)malloc(sizeof(struct node));
    ptr->data = data;
    ptr->next = head;
   
    ptr->prev = NULL;
    head->prev = ptr;
  
    head = ptr;
    return head;
}
int main()
{
    struct node *head;
    struct node *second;
    struct node *third;
    struct node *fourth;

    // Allocate memory for nodes in the linked list in Heap
    head = (struct node *)malloc(sizeof(struct node));
   second = (struct node *)malloc(sizeof(struct node));
    third = (struct node *)malloc(sizeof(struct node));
    fourth = (struct node *)malloc(sizeof(struct node));

    //Link first and second node.
    head->data = 11;
    head->prev = NULL;
    head->next = second;

    // Link second and third
    second->data = 12;
    second->prev = head;
    second->next = third;

    // Link third and fourth
    third->data = 13;
    third->prev = second;
    third->next = fourth;

    // Terminate the linked list;
    fourth->data = 14;
    fourth->prev = third;
    fourth->next = NULL;
    printf("Before insertion\n");
    linkedlist(head);
    head = insertatfirst(head,101);
   printf("After insertion\n");
    linkedlist(head);





    return 0;

}