C 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.

Here is a source code of the C program to implement doubly linked list using singly linked list. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

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/*
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 * C Program to Implement Doubly Linked List using Singly Linked List

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 */
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#include <stdio.h>
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#include <stdlib.h>
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struct node
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{
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    int num;
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    struct node *next;
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};
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void create(struct node **);
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void move (struct node *);
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void release(struct node **);
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void display(struct node *);
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int main()
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{
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    struct node *p = NULL, *q = NULL;
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    int result, count;
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    printf("Enter data into the list\n");

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    create(&p);
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    printf("Displaying list:\n");
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    display(p);
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    move(p);
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    release (&p);
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    return 0;
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}
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```
 
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void move(struct node *head)
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{
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    struct node *p, *q;
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    int ch;
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    p = q = head;
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    printf("\nPointer at %d\n", head->num);

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

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        scanf("%d", &ch);
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        switch(ch)
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        {
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        case 1: if(q->next != NULL)
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                {
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                    q = q->next;
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                    printf("\nPointer at %d\n", q->num);

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

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                }
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                break;
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        case 2: while (p->next != q)
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                {
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                    p = p->next;
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                }
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                if (p == q)
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                {
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                    printf("\nPointer at first node %d. Cannot move behind.\n", q->num);

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                }
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                else
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                {
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                    q = p;
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                    p = head;
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                    printf("\nPointer at %d\n", q->num);

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                }
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                break;
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        case 3: return;
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        default: printf("\nInvalid choice entered. Try again\n");

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        }
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    } while (1);
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}
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```
 
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void create(struct node **head)
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{
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    int c, ch;
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    struct node *temp, *rear;
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    do
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    {
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        printf("Enter number: ");
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        scanf("%d", &c);
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        temp = (struct node *)malloc(sizeof(struct node));

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        temp->num = c;
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        temp->next = NULL;
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        if (*head == NULL)
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        {
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            *head = temp;
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        }
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        else
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        {
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            rear->next = temp;
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        }
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        rear = temp;
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        printf("Do you wish to continue [1/0]: ");

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        scanf("%d", &ch);
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    } while (ch != 0);
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    printf("\n");
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}
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```
 
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void display(struct node *head)
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{
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    while (head != NULL)
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```
    {
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        printf("%d\t", head->num);
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        head = head->next;
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    }
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    printf("\n");
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}
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```
 
```
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void release(struct node **head)
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{
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    struct node *temp;
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    while ((*head) != NULL)
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    {
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        temp = *head;
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        (*head) = (*head)->next;
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        free(temp);
```
```
    }
```
```
}
```

$ cc singledouble.c 
$ ./a.out
Enter data into the list
Enter number: 2
Do you wish to continue [1/0]: 1
Enter number: 4
Do you wish to continue [1/0]: 1
Enter number: 6
Do you wish to continue [1/0]: 1
Enter number: 8
Do you wish to continue [1/0]: 1 
Enter number: 10
Do you wish to continue [1/0]: 0
 
Displaying list:
2	4	6	8	10	
 
Pointer at 2
Select option:
1. Move front
2. Move back
3. Exit
Your choice: 1
 
Pointer at 4
Select option:
1. Move front
2. Move back
3. Exit
Your choice: 1
 
Pointer at 6
Select option:
1. Move front
2. Move back
3. Exit
Your choice: 2
 
Pointer at 4
Select option:
1. Move front
2. Move back
3. Exit
Your choice: 2
 
Pointer at 2
Select option:
1. Move front
2. Move back
3. Exit
Your choice: 3