#include <iostream>

#define SIZE 20

using namespace std;

class Deque {

private:

int deq[SIZE];

int start;

int tail;

public:

Deque() {

start = tail = 0;

}

void Push_back(int data) {

if (!IsFull()) {

deq[(tail + SIZE) % SIZE] = data;

++tail;

return;

}

cout << "队列已满，无法插入！" << endl;

}

int Pop_front() {

if (IsEmpty()) {

cout << "空队列，无法输出元素！";

return -1;

}

int data = deq[(start + SIZE) % SIZE];

++start;

return data;

}

int Size() {

return (tail - start + SIZE) % SIZE;

}

bool IsEmpty() {

return Size() == 0;

}

bool IsFull() {

return Size() == SIZE - 1;

}

};

int main()

{

Deque* deq = new Deque();

for (int i = 0; i < 21; i++) {

deq->Push_back(i);

cout << "Size is " << deq->Size() << endl;

}

for (int i = 0; i < 21; i++) {

cout << deq->Pop_front() << " ";

if ((i + 1) % 5 == 0) cout << endl;

}

delete deq;

return 0;

}