void queue_insert(queue *q, data v) {
    q->rear = (q->rear + 1) % q->capacity;
    if (q->size == q->rear) {
        q->capacity <<= 1; // double the capacity of the circular queue
        q->values = realloc(q->values, sizeof(data) * q->capacity);
    }
    q->values[q->rear] = v;
    q->size++;
    return;
}
the queue is a circular queue. Here is the structure:
typedef struct {
    unsigned int capacity; ///< current capacity of the queue.
    int front; ///< index of front element of the queue.
    int rear; ///< index of next rear element of the queue.
    int size; ///< count of number of values in the queue.
    data *values; ///< array of data values.
} queue;