{"id":545,"date":"2024-10-19T13:52:14","date_gmt":"2024-10-19T08:22:14","guid":{"rendered":"https:\/\/codexplained.in\/?p=545"},"modified":"2025-11-24T15:33:52","modified_gmt":"2025-11-24T10:03:52","slug":"implement-circular-queue-using-linked-list","status":"publish","type":"post","link":"https:\/\/codexplained.in\/?p=545","title":{"rendered":"Implement Circular Queue using Linked List"},"content":{"rendered":"
\n#include <stdio.h>\n#include <stdlib.h>\n\n\/\/ Node structure\nstruct Node {\n    int data;\n    struct Node* next;\n};\n\n\/\/ Front and rear pointers\nstruct Node *front = NULL;\nstruct Node *rear = NULL;\n\n\/\/ Function to add an element to the queue (enqueue)\nvoid enqueue(int value) {\n    struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));\n    newNode->data = value;\n    newNode->next = NULL;\n\n    \/\/ Check if queue is empty\n    if (front == NULL) {\n        front = newNode;\n    } else {\n        rear->next = newNode;\n    }\n    rear = newNode;\n    rear->next = front; \/\/ Point rear's next to front to make it circular\n    printf("%d enqueued to the queue.\\n", value);\n}\n\n\/\/ Function to remove an element from the queue (dequeue)\nvoid dequeue() {\n    if (front == NULL) {\n        printf("Queue is empty. Cannot dequeue.\\n");\n        return;\n    }\n\n    \/\/ Case: Only one element in the queue\n    if (front == rear) {\n        printf("%d dequeued from the queue.\\n", front->data);\n        free(front);\n        front = rear = NULL;\n    } else {\n        struct Node* temp = front;\n        front = front->next;\n        rear->next = front; \/\/ Maintain circular link\n        printf("%d dequeued from the queue.\\n", temp->data);\n        free(temp);\n    }\n}\n\n\/\/ Function to display the elements of the queue\nvoid display() {\n    if (front == NULL) {\n        printf("Queue is empty.\\n");\n        return;\n    }\n\n    struct Node* temp = front;\n    printf("Queue elements: ");\n    do {\n        printf("%d ", temp->data);\n        temp = temp->next;\n    } while (temp != front);\n    printf("\\n");\n}\n\n\/\/ Main function to test the circular queue\nint main() {\n    enqueue(10);\n    enqueue(20);\n    enqueue(30);\n    display();\n    dequeue();\n    display();\n    enqueue(40);\n    display();\n    dequeue();\n    display();\n\n    return 0;\n}\n\n<\/pre><\/div>\n\n\n
Explanation :<\/h3>\n\n\n\n
    \n
  1. Node Structure<\/strong>:\n
      \n
    • Each node has an integer data<\/code> and a pointer next<\/code> that points to the next node.<\/li>\n\n\n\n
    • struct Node<\/code> is used to define this structure.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
    • Front and Rear Pointers<\/strong>:\n
        \n
      • front<\/code> points to the first element in the queue.<\/li>\n\n\n\n
      • rear<\/code> points to the last element in the queue.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
      • Enqueue Operation<\/strong>:\n
          \n
        • A new node is created using malloc<\/code>.<\/li>\n\n\n\n
        • If the queue is empty (front<\/code> is NULL<\/code>), the front<\/code> and rear<\/code> both point to this new node.<\/li>\n\n\n\n
        • Otherwise, the new node is added after the rear<\/code>, and rear<\/code> is updated to this new node.<\/li>\n\n\n\n
        • To maintain the circular nature, rear->next<\/code> is set to front<\/code>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
        • Dequeue Operation<\/strong>:\n
            \n
          • If the queue is empty (front<\/code> is NULL<\/code>), print an error message.<\/li>\n\n\n\n
          • If there is only one element (front == rear<\/code>), free the node and set front<\/code> and rear<\/code> to NULL<\/code>.<\/li>\n\n\n\n
          • Otherwise, remove the front<\/code> node, update front<\/code> to front->next<\/code>, and set rear->next<\/code> to front<\/code> to maintain the circular link.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
          • Display Function<\/strong>:\n
              \n
            • If the queue is empty, print a message.<\/li>\n\n\n\n
            • Otherwise, use a temporary pointer temp<\/code> to traverse the queue starting from front<\/code>, and print each node\u2019s data<\/code> until we reach front<\/code> again.<\/li>\n<\/ul>\n<\/li>\n\n\n\n
            • Main Function<\/strong>:\n
                \n
              • Performs a few enqueue<\/code> and dequeue<\/code> operations and displays the queue’s contents to demonstrate how the circular queue works.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n
                10 enqueued to the queue.\n20 enqueued to the queue.\n30 enqueued to the queue.\nQueue elements: 10 20 30 \n10 dequeued from the queue.\nQueue elements: 20 30 \n40 enqueued to the queue.\nQueue elements: 20 30 40 \n20 dequeued from the queue.\nQueue elements: 30 40 <\/code><\/pre>\n\n\n\n
                How the Circular Nature Works<\/h3>\n\n\n\n
                  \n
                • When adding elements, the rear->next<\/code> always points back to front<\/code>, creating a circle.<\/li>\n\n\n\n
                • When removing elements, even as front<\/code> moves forward, rear<\/code> still points back to the updated front<\/code>, keeping the circular link intact.<\/li>\n\n\n\n
                • This structure allows the queue to wrap around in a circular manner, hence the name “circular queue.”<\/li>\n<\/ul>\n