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Program to Implement Doubly Linked List using Singly Linked List



Program to Implement Doubly Linked List using Singly Linked List

This C Program implements doubly linked list using singly linked list. It makes use of 2 pointers, one points at the current node, other points at the head. When user requests to move back, the pointer from head travels to a previous node of the current pointer. The pointer to previous node is the resulting node.

    #include <stdio.h>

    #include <stdlib.h>

    struct node

    {

        int j;

        struct node *next;

    };

    void create(struct node **);

    void move (struct node *);

    void release(struct node **);

    void display(struct node *);

    int main()

    {

        struct node *p = NULL, *q = NULL;

        int result, count;

        printf("Enter data into the list\n");

        create(&p);

        printf("Displaying list:\n");

        display(p);

        move(p);

        release (&p);

        return 0;

    }

    void move(struct node *head)

    {

        struct node *p, *q;

        int ch;

        p = q = head;

        printf("\nPointer at %d\n", head->j);

        do

        {

            printf("Select option:\n1. Move front\n2. Move back\n3. Exit\nYour choice: ");

            scanf("%d", &ch);

            switch(ch)

            {

            case 1: if(q->next != NULL)

                    {

                        q = q->next;

                        printf("\nPointer at %d\n", q->j);

                    }

                    else

                    {

                        printf("\nPointer at last node %d. Cannot move ahead.\n", q->j);

                    }

                    break;

            case 2: while (p->next != q)

                    {

                        p = p->next;

                    }

                    if (p == q)

                    {

                        printf("\nPointer at first node %d. Cannot move behind.\n", q->j);

                    }

                    else

                    {

                        q = p;

                        p = head;

                        printf("\nPointer at %d\n", q->j);

                    }

                    break;

            case 3: return;

            default: printf("\nInvalid choice entered. Try again\n");

            }

        } while (1);

    }

    void create(struct node **head)

    {

        int c, ch;

        struct node *temp, *rear;

        do

        {

            printf("Enter number: ");

            scanf("%d", &c);

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

            temp->j = c;

            temp->next = NULL;

            if (*head == NULL)

            {

                *head = temp;

            }

            else

            {

                rear->next = temp;

            }

            rear = temp;

            printf("Do you wish to continue [1/0]: ");

            scanf("%d", &ch);

        } while (ch != 0);

        printf("\n");

    }

    void display(struct node *head)

    {

        while (head != NULL)

        {

            printf("%d\t", head->j);

            head = head->next;

        }

        printf("\n");

    }

    void release(struct node **head)

    {

        struct node *temp;

        while ((*head) != NULL)

        {

            temp = *head;

            (*head) = (*head)->next;

            free(temp);

        }

    }