如何用c实现一个循环队列

下面是一个简单的循环队列的C语言代码实现：

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

#define MAXSIZE 5

typedef struct {
    int data[MAXSIZE];
    int front;
    int rear;
} Queue;

Queue* createQueue() {
    Queue* q = (Queue*) malloc(sizeof(Queue));
    q->front = -1;
    q->rear = -1;
    return q;
}

int isFull(Queue* q) {
    return (q->front == 0 && q->rear == MAXSIZE - 1) || (q->rear == (q->front - 1) % (MAXSIZE - 1));
}

int isEmpty(Queue* q) {
    return q->front == -1;
}

void enqueue(Queue* q, int value) {
    if (isFull(q)) {
        printf("Queue is full.\n");
        return;
    }

    if (q->front == -1) {
        q->front = q->rear = 0;
        q->data[q->rear] = value;
    } else if (q->rear == MAXSIZE - 1 && q->front != 0) {
        q->rear = 0;
        q->data[q->rear] = value;
    } else {
        q->rear++;
        q->data[q->rear] = value;
    }
}

int dequeue(Queue* q) {
    if (isEmpty(q)) {
        printf("Queue is empty.\n");
        return -1;
    }

    int value = q->data[q->front];
    q->data[q->front] = -1;

    if (q->front == q->rear) {
        q->front = -1;
        q->rear = -1;
    } else if (q->front == MAXSIZE - 1) {
        q->front = 0;
    } else {
        q->front++;
    }

    return value;
}

int main() {
    Queue* q = createQueue();

    enqueue(q, 1);
    enqueue(q, 2);
    enqueue(q, 3);
    enqueue(q, 4);
    enqueue(q, 5);
    enqueue(q, 6);
    printf("Dequeued item: %d\n", dequeue(q));
    printf("Dequeued item: %d\n", dequeue(q));
    printf("Dequeued item: %d\n", dequeue(q));
    printf("Dequeued item: %d\n", dequeue(q));
    printf("Dequeued item: %d\n", dequeue(q));
    printf("Dequeued item: %d\n", dequeue(q));

    return 0;
}

这个循环队列实现了enqueue和dequeue操作。enqueue操作将元素添加到队列的尾部，dequeue操作将元素从队列的头部删除并返回。如果队列已满，则enqueue操作将不起作用，如果队列为空，则dequeue操作将不起作用。