circular_queue.c

#include <stdio.h>

#define CAPACITY 5

typedef struct {
    int data[CAPACITY];
    int front, rear, count;
} Queue;

void init(Queue *q) {
    q->front = 0;
    q->rear = -1;
    q->count = 0;
}   

int isEmpty(Queue *q) {
    return q->count == 0;
}

int isFull(Queue *q) {
    return q->count == CAPACITY;
}

/* --- enqueue --- */ 
void enqueue(Queue *q, int value) {
    if(isFull(q)){
        printf("Full! Could not add %d\n", value);
        return;
    }
    q->rear = (q->rear+1) % CAPACITY ;
    q->data[q->rear] = value;
    q->count++;
    printf("Added : %d (rear= %d) (count= %d)\n", value,q->rear, q->count);
    return;
}

/* --- dequeue --- */
int dequeue(Queue *q) {
    if(isEmpty(q)){
        printf("Empty ! ");
        return -1;
    }
    int result = q->data[q->front];
    q->front = (q->front+1) % CAPACITY;
    q->count--;
    return result;
    // hint: front = (front + 1) % CAPACITY;
}

int main(void) {
    Queue q;
    init(&q);

    enqueue(&q, 10);
    enqueue(&q, 20);
    enqueue(&q, 30);
    enqueue(&q, 40);
    enqueue(&q, 50);

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

    enqueue(&q, 60);   
    enqueue(&q, 70);
    enqueue(&q, 80);   

    return 0;
}