Question

Write a C function that iterates through a singly linked list and converts it to a doubly linked list. Your solution must NOT create a second list. You must come up with the appropriate parameters and return type. Note: the nodes in the singly linked list have a field for a previous pointer, but that field has not initially been set in any of the nodes. You must do this as part of your solution!

Answer 1

code:-

#include <stdio.h>
#include <stdlib.h>
//declarinf structure for Linked list
struct node
{
    struct node *next,*prev;
    int n;
}*h,*temp,*temp1,*temp2,*temp4;
int count = 0;

int main()
{
    int ch;

    h = NULL;
    temp = temp1 = NULL;
    int data,x;
    //constructing single linked list
  
    printf("Enter number of nodes:");
    scanf("%d",&x);
    temp =(struct node *)malloc(1*sizeof(struct node));//creating head node
        printf("\n Enter value to node : ");
        scanf("%d", &data);
        temp->n = data;
        temp->next = NULL;
        h=temp;
   //creating remaining nodes for linked list
    for(int i=1;i<x;i++){
      temp1 =(struct node *)malloc(1*sizeof(struct node));
        printf("\n Enter value to node : ");
        scanf("%d", &data);
        temp1->n = data;
        temp1->next = NULL;
        temp->next = temp1;
        temp=temp1;
   }
   //printing normal single linked list
   temp = h;

    if (temp == NULL)
    {
        printf("List empty to display \n");
        return 0;
    }
    printf("\nSingle Linked list elements from begining : \n");

    while (temp->next != NULL)
    {
        printf(" %d ", temp->n);
        temp = temp->next;
    }
    printf(" %d ", temp->n);
  
    //converting Single linked list into double linked list
    temp = h;
    temp->prev=NULL;
    while (temp->next != NULL)
    {
       temp1=temp;
        temp = temp->next;
        temp->prev=temp1;
    }

   printf("\ndouble Linked list elements from begining to end : \n");
   temp = h;
    while (temp->next != NULL)
    {
        printf(" %d ", temp->n);
        temp = temp->next;
    }
    printf(" %d ", temp->n);
    printf("\ndouble Linked list elements from end to begining: \n");
    while (temp->prev != NULL)
    {
        printf(" %d ", temp->n);
        temp = temp->prev;
    }
    printf(" %d ", temp->n);
    return 0;
}

output:

Thank you