Implement Queue using Linked List

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

// Structure to represent a node in the queue
struct Node {
    int data;
    struct Node* next;
};

// Structure to represent the queue with pointers to the front and rear
struct Queue {
    struct Node *front, *rear;
};

// Function to create a new node with the given data
struct Node* newNode(int data) {
    struct Node* temp = (struct Node*)malloc(sizeof(struct Node));
    temp->data = data;
    temp->next = NULL;
    return temp;
}

// Function to create an empty queue
struct Queue* createQueue() {
    struct Queue* q = (struct Queue*)malloc(sizeof(struct Queue));
    q->front = q->rear = NULL;
    return q;
}

// Function to add an element to the queue
void enqueue(struct Queue* q, int data) {
    // Create a new node
    struct Node* temp = newNode(data);
    
    // If the queue is empty, the new node will be the front and rear
    if (q->rear == NULL) {
        q->front = q->rear = temp;
        printf("Enqueued %d to the queue.\n", data);
        return;
    }

    // Attach the new node at the end of the queue and change the rear
    q->rear->next = temp;
    q->rear = temp;
    printf("Enqueued %d to the queue.\n", data);
}

// Function to remove an element from the queue
void dequeue(struct Queue* q) {
    // If the queue is empty, there is nothing to dequeue
    if (q->front == NULL) {
        printf("Queue is empty, nothing to dequeue.\n");
        return;
    }

    // Store the previous front and move the front one node ahead
    struct Node* temp = q->front;
    q->front = q->front->next;

    // If the front becomes NULL, then the queue is empty, so set rear to NULL
    if (q->front == NULL) {
        q->rear = NULL;
    }

    printf("Dequeued %d from the queue.\n", temp->data);
    free(temp);
}

// Function to display the current elements of the queue
void displayQueue(struct Queue* q) {
    struct Node* temp = q->front;
    if (temp == NULL) {
        printf("Queue is empty.\n");
        return;
    }

    printf("Queue elements: ");
    while (temp != NULL) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("\n");
}

// Main function to demonstrate queue operations
int main() {
    struct Queue* q = createQueue();

    enqueue(q, 10);
    enqueue(q, 20);
    enqueue(q, 30);

    displayQueue(q);

    dequeue(q);
    displayQueue(q);

    dequeue(q);
    dequeue(q);
    dequeue(q);

    return 0;
}