C++循环顺序队列

#include 

using namespace std;
struct SqQueue
{
    char data[20];
    int front,rear;
};
bool SqQueueEmpty(SqQueue q)
{
    return (q.front==q.rear);
}
bool enQueue(SqQueue& q,char e)
{
    if((q.rear+1)%20==q.front)
        return false;
    q.rear=(q.rear+1)%20;
    q.data[q.rear]=e;
    return true;
}
bool deQueue(SqQueue& q,char& e)
{
    if(q.front==q.rear)
        return false;
    q.front=(q.front+1)%20;
    e=q.data[q.front];
    return true;
}
int main()
{
    SqQueue q;
    q.front=q.rear=0;
    char e,a[5]= {'a','b','c','d'};
    for(int i=0; i<5; i++)
    {
        if(!enQueue(q,a[i]))
            break;
    }
    if(SqQueueEmpty(q))
        cout<<"空队。\n";
    else
        cout<<"非空队。\n";
    while(deQueue(q,e))
    {
        cout<