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.

```
/*
```

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

```
 */
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
struct node
```
```
{
```
```
    int num;
```
```
    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->num);

```
    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->num);

```
                }
```
```
                else
```
```
                {
```

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

```
                }
```
```
                break;
```
```
        case 2: while (p->next != q)
```
```
                {
```
```
                    p = p->next;
```
```
                }
```
```
                if (p == q)
```
```
                {
```

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

```
                }
```
```
                else
```
```
                {
```
```
                    q = p;
```
```
                    p = head;
```

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

```
                }
```
```
                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->num = 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->num);
```
```
        head = head->next;
```
```
    }
```
```
    printf("\n");
```
```
}
```
```
 
```
```
void release(struct node **head)
```
```
{
```
```
    struct node *temp;
```
```
    while ((*head) != NULL)
```
```
    {
```
```
        temp = *head;
```
```
        (*head) = (*head)->next;
```
```
        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

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