#include <stdio.h>
#include <stdlib.h>
 
// Structure for Queue
struct Queue {
    int *arr;
    int front;
    int rear;
    int capacity;
};
 
// Function prototypes
void initialize(struct Queue *queue, int capacity);
int isFull(struct Queue *queue);
int isEmpty(struct Queue *queue);
void enqueue(struct Queue *queue, int value);
int dequeue(struct Queue *queue);
int peek(struct Queue *queue);
void display(struct Queue *queue);
 
int main() {
    struct Queue queue;
    int capacity, choice, value;
 
    printf("Enter the maximum size of queue: ");
    scanf("%d", &capacity);
 
    initialize(&queue, capacity);
 
    do {
        printf("\n--- Queue Operations Menu ---\n");
        printf("1. Enqueue (Insert)\n");
        printf("2. Dequeue (Remove)\n");
        printf("3. Peek (Front Element)\n");
        printf("4. Display Queue\n");
        printf("0. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
 
        switch (choice) {
            case 1:
                printf("Enter value to enqueue: ");
                scanf("%d", &value);
                enqueue(&queue, value);
                break;
            case 2:
                value = dequeue(&queue);
                if (value != -1)
                    printf("Dequeued value: %d\n", value);
                break;
            case 3:
                value = peek(&queue);
                if (value != -1)
                    printf("Front element: %d\n", value);
                break;
            case 4:
                display(&queue);
                break;
            case 0:
                printf("Exiting program.\n");
                break;
            default:
                printf("Invalid choice!\n");
        }
    } while (choice != 0);
 
    // Free dynamically allocated memory
    free(queue.arr);
 
    return 0;
}
 
// Function to initialize the queue
void initialize(struct Queue *queue, int capacity) {
    queue->capacity = capacity;
    queue->front = -1;
    queue->rear = -1;
    queue->arr = (int *) malloc(queue->capacity * sizeof(int));
 
    if (queue->arr == NULL) {
        printf("Memory allocation failed!\n");
        exit(1);
    }
}
 
// Check if queue is full
int isFull(struct Queue *queue) {
    return queue->rear == queue->capacity - 1;
}
 
// Check if queue is empty
int isEmpty(struct Queue *queue) {
    return queue->front == -1 || queue->front > queue->rear;
}
 
// Enqueue operation
void enqueue(struct Queue *queue, int value) {
    if (isFull(queue)) {
        printf("Queue Overflow! Cannot enqueue %d\n", value);
        return;
    }
 
    if (queue->front == -1)
        queue->front = 0;
 
    queue->arr[++queue->rear] = value;
    printf("%d enqueued to queue.\n", value);
}
 
// Dequeue operation
int dequeue(struct Queue *queue) {
    if (isEmpty(queue)) {
        printf("Queue Underflow! No elements to dequeue.\n");
        return -1;
    }
 
    int value = queue->arr[queue->front++];
    if (queue->front > queue->rear)
        queue->front = queue->rear = -1;
 
    return value;
}
 
// Peek (front element)
int peek(struct Queue *queue) {
    if (isEmpty(queue)) {
        printf("Queue is empty!\n");
        return -1;
    }
    return queue->arr[queue->front];
}
 
// Display all elements
void display(struct Queue *queue) {
    if (isEmpty(queue)) {
        printf("Queue is empty!\n");
        return;
    }
 
    printf("\nQueue elements (Front to Rear):\n");
    for (int i = queue->front; i <= queue->rear; i++)
        printf("%d ", queue->arr[i]);
    printf("\n");
}