Queue (FIFO)

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

#define MAX 100 // Maximum size of the queue

typedef struct {
    int front, rear, size;
    int items[MAX];
} Queue;

// Initialize the queue
void initQueue(Queue* q) {
    q->front = 0;
    q->rear = -1;
    q->size = 0;
}

// Check if the queue is empty
int isEmpty(Queue* q) {
    return q->size == 0;
}

// Check if the queue is full
int isFull(Queue* q) {
    return q->size == MAX;
}

// Enqueue an item into the queue
void enqueue(Queue* q, int item) {
    if (isFull(q)) {
        printf("Queue overflow\n");
        return;
    }
    q->rear = (q->rear + 1) % MAX;
    q->items[q->rear] = item;
    q->size++;
}

// Dequeue an item from the queue
int dequeue(Queue* q) {
    if (isEmpty(q)) {
        printf("Queue underflow\n");
        return -1; // Error code
    }
    int item = q->items[q->front];
    q->front = (q->front + 1) % MAX;
    q->size--;
    return item;
}

// Peek the front item of the queue
int peek(Queue* q) {
    if (isEmpty(q)) {
        printf("Queue is empty\n");
        return -1; // Error code
    }
    return q->items[q->front];
}

// Print queue contents
void printQueue(Queue* q) {
    if (isEmpty(q)) {
        printf("Queue is empty\n");
        return;
    }
    int i = q->front;
    for (int j = 0; j < q->size; j++) {
        printf("%d\n", q->items[i]);
        i = (i + 1) % MAX;
    }
}

int main() {
    Queue q;
    initQueue(&q);

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

    printf("Queue contents:\n");
    printQueue(&q);

    printf("Dequeued: %d\n", dequeue(&q));
    printf("Front item: %d\n", peek(&q));

    return 0;
}