C Program to Implement Doubly Linked List using Singly Linked List

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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.

  1. /*
  2.  * C Program to Implement Doubly Linked List using Singly Linked List 
  3.  */
  4. #include <stdio.h>
  5. #include <stdlib.h>
  6.  
  7. struct node
  8. {
  9.     int num;
  10.     struct node *next;
  11. };
  12.  
  13. void create(struct node **);
  14. void move (struct node *);
  15. void release(struct node **);
  16. void display(struct node *);
  17.  
  18. int main()
  19. {
  20.     struct node *p = NULL, *q = NULL;
  21.     int result, count;
  22.  
  23.     printf("Enter data into the list\n");
  24.     create(&p);
  25.     printf("Displaying list:\n");
  26.     display(p);
  27.     move(p);
  28.     release (&p);
  29.  
  30.     return 0;
  31. }
  32.  
  33. void move(struct node *head)
  34. {
  35.     struct node *p, *q;
  36.     int ch;
  37.  
  38.     p = q = head;
  39.     printf("\nPointer at %d\n", head->num);
  40.     do
  41.     {
  42.         printf("Select option:\n1. Move front\n2. Move back\n3. Exit\nYour choice: ");
  43.         scanf("%d", &ch);
  44.         switch(ch)
  45.         {
  46.         case 1: if(q->next != NULL)
  47.                 {
  48.                     q = q->next;
  49.                     printf("\nPointer at %d\n", q->num);
  50.                 }
  51.                 else
  52.                 {
  53.                     printf("\nPointer at last node %d. Cannot move ahead.\n", q->num);
  54.                 }
  55.                 break;
  56.         case 2: while (p->next != q)
  57.                 {
  58.                     p = p->next;
  59.                 }
  60.                 if (p == q)
  61.                 {
  62.                     printf("\nPointer at first node %d. Cannot move behind.\n", q->num);
  63.                 }
  64.                 else
  65.                 {
  66.                     q = p;
  67.                     p = head;
  68.                     printf("\nPointer at %d\n", q->num);
  69.                 }
  70.                 break;
  71.         case 3: return;
  72.         default: printf("\nInvalid choice entered. Try again\n");
  73.         }
  74.     } while (1);
  75. }
  76.  
  77. void create(struct node **head)
  78. {
  79.     int c, ch;
  80.     struct node *temp, *rear;
  81.  
  82.     do
  83.     {
  84.         printf("Enter number: ");
  85.         scanf("%d", &c);
  86.         temp = (struct node *)malloc(sizeof(struct node));
  87.         temp->num = c;
  88.         temp->next = NULL;
  89.         if (*head == NULL)
  90.         {
  91.             *head = temp;
  92.         }
  93.         else
  94.         {
  95.             rear->next = temp;
  96.         }
  97.         rear = temp;
  98.         printf("Do you wish to continue [1/0]: ");
  99.         scanf("%d", &ch);
  100.     } while (ch != 0);
  101.     printf("\n");
  102. }
  103.  
  104. void display(struct node *head)
  105. {
  106.     while (head != NULL)
  107.     {
  108.         printf("%d\t", head->num);
  109.         head = head->next;
  110.     }
  111.     printf("\n");
  112. }
  113.  
  114. void release(struct node **head)
  115. {
  116.     struct node *temp;
  117.     while ((*head) != NULL)
  118.     {
  119.         temp = *head;
  120.         (*head) = (*head)->next;
  121.         free(temp);
  122.     }
  123. }

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$ 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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