Convert singly linked list into circular linked list using C program

In this tutorial, we will learn how to convert singly linked list into circular linked list using C program? By Piyas Mukherjee Last updated : August 02, 2023

Input

A singly linked list whose address of the first node is stored in a pointer, say head

Output

The same circular linked list.

Data structure used

Singly linked list where each node contains a data element say data, and the address of the immediate next node say next, with Head holding the address of the first node.

Pseudo Code

Begin
temp=head
while(temp->next!=NULL)
	begin
	temp=temp->next
	end While
//link head to the next of last node 
temp->next=head
End

C program to convert singly linked list into circular linked list

#include <stdio.h>
#include <stdlib.h>

typedef struct list {
    int data;
    struct list* next;
} node;

void display(node* temp)
{
    //now temp1 is head basically
    node* temp1 = temp;
    printf("The list is as follows :\n%d->", temp->data);
    temp = temp->next;
    //which not circle back to head node
    while (temp != temp1) {
        printf("%d->", temp->data);
        temp = temp->next;
    }
    printf("%d\n", temp1->data);

    return;
}

// Main Code
int main()
{
    node *head = NULL, *temp, *temp1;
    int choice, count = 0, key;

    //Taking the linked list as input
    do {
        temp = (node*)malloc(sizeof(node));
        if (temp != NULL) {
            printf("\nEnter the element in the list : ");
            scanf("%d", &temp->data);
            temp->next = NULL;
            if (head == NULL) {
                head = temp;
            }
            else {
                temp1 = head;
                while (temp1->next != NULL) {
                    temp1 = temp1->next;
                }
                temp1->next = temp;
            }
        }
        else {
            printf("\nMemory not avilable...node allocation is not possible");
        }
        printf("\nIf you wish to add m ore data on the list enter 1 : ");
        scanf("%d", &choice);
    } while (choice == 1);

    //In order to convert a singly linked list to a
    //circular singly linked list we just need to copy
    //the address of the head node to the next of the last node
    temp = head;
    
    //travarsing to the last node
    while (temp->next != NULL) {
        temp = temp->next;
    }
    
    //the address of the head is copied to the next part
    //of the last node.....now it is a circular singly linked list
    temp->next = head;
    
    display(head);

    return 0;
}

Output

Enter the element in the list : 1

If you wish to add m ore data on the list enter 1 : 1

Enter the element in the list : 2

If you wish to add m ore data on the list enter 1 : 1

Enter the element in the list : 3

If you wish to add m ore data on the list enter 1 : 1

Enter the element in the list : 4

If you wish to add m ore data on the list enter 1 : 1

Enter the element in the list : 5

If you wish to add m ore data on the list enter 1 : 0
The list is as follows :
1->2->3->4->5->1