C program to Implement Circular Linked List

Circular Linked List

In the circular linked list the last node of the list contains the address of the first node and forms a circular chain.

Here is source code of the C Program to Implement Circular Linked List using Dynamic Memory Allocation. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

#include<stdio.h>

struct linked_list_node{
    int num;
    struct linked_list_node *next;
};

typedef struct linked_list_node snode;

snode *first = NULL;
snode *last = NULL;

void insertNode(int value);
void insertAtFirst(int value);
void deleteFirst();
void deleteLast();
snode *createNode(int value);
void display();

void main()
{
    int choice, nValue;
    char ch='y';

    while (ch == 'y')
    {
        printf("\n------------------------------------------------------------\n");
        printf("\tCircular Linked List\n");
        printf("------------------------------------------------------------\n");

        printf("\n1. Insert a node at last\n");
        printf("2. Insert a node at first\n");
        printf("3. Delete First Node\n");
        printf("4. Delete Last Node\n");
        printf("5.Display contents of list\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch(choice)
        {
            case 1:
                    printf("\nInserting a new node at last.....\n");
                    printf("Enter the value of node: ");
                    scanf("%d", &nValue);
                    insertNode(nValue);
                    break;
            case 2:
                    printf("\nInserting a node at first.....\n");
                    printf("Enter the value of node: ");
                    scanf("%d", &nValue);
                    insertAtFirst(nValue);
                    break;
            case 3:
                    printf("\nDeleteing first node.....\n");
                    deleteFirst();
                    break;
            case 4:
                    printf("\nDeleteing last node.....\n");
                    deleteLast();
                    break;
            case 5:
                    printf("\nContents of linked list are as follows\n");
                    display();
                    break;
            default:
                    printf("\nInvalid choice!!!\n");
        }

        printf("\nDo you want to continue(y/n)?" );
        scanf(" %c", &ch);
    }
}

snode *createNode(int value)
{
    snode *newNode;

    newNode = (snode *)malloc(sizeof(snode));
    newNode->num = value;
    newNode->next = NULL;
    return newNode;
}

void insertNode(int value)
{
    snode *newNode;
    newNode = createNode(value);

    if (first == last && first == NULL)
    {
        newNode->next = first;
        first = last = newNode;
    }
    else
    {
        last->next = newNode;
        newNode->next = first;
        last = newNode;
    }
}

void insertAtFirst(int value)
{
    snode *newNode;
    newNode = createNode(value);

    newNode->next = first;
    last->next = newNode;
    first = newNode;
}

void deleteFirst()
{
    if (first == NULL)
    {
        printf("List is empty!!!\n");
    }
    else if (first == last)
    {
        first = last = NULL;
        printf("Node successfully deleted!!!\n");
    }
    else
    {
        first = first->next;
        printf("Node successfully deleted!!!\n");
    }
}

void deleteLast()
{
    snode *temp;
    if (first == NULL)
    {
        printf("List is empty!!!\n");
    }
    else if (first == last)
    {
        first = last = NULL;
        printf("Node successfully deleted!!!\n");
    }
    else
    {
        temp = first;
        while (temp)
        {
            if (temp->next == last)
            {
                break;
            }
            temp = temp->next;
        }
        last = temp;
        printf("Node successfully deleted!!!\n");
    }
}

void display()
{
    snode *temp = first;

    if (first == NULL)
    {
        printf("List is empty!!!\n");
        return;
    }

    while (temp != last)
    {
        printf("%d-->", temp->num);
        temp = temp->next;
    }
    printf("%d", last->num);
}

Output:

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 1

Inserting a new node at last.....
Enter the value of node: 5

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 1

Inserting a new node at last.....
Enter the value of node: 6

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 5

Contents of linked list are as follows
5-->6

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 2

Inserting a node at first.....
Enter the value of node: 4

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 5

Contents of linked list are as follows
4-->5-->6

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 3

Deleting first node.....
Node successfully deleted!!!

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 5

Contents of linked list are as follows
5-->6

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5.Display contents of list

Enter your choice: 4

Deleteing last node.....
Node successfully deleted!!!

Do you want to continue(y/n)?y

----------------------------------------------------------
    Circular Linked List
----------------------------------------------------------

1. Insert a node at last
2. Insert a node at first
3. Delete First Node
4. Delete Last Node
5. Display contents of list

Enter your choice: 5

Contents of linked list are as follows
5

Do you want to continue(y/n)?

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