// 循环队列的实现

#include <iostream>
#include <fstream>
using namespace std;

#define MAXQSIZE	100
#define OK			1
#define ERROR		0
#define OVERFLOW	-1

typedef char QElemType;
typedef char SElemType;
typedef int  Status;

// 定义队列结构体
struct SqQueue
{
	QElemType* base;	// 分配内存空间
	int front;			// 头指针
	int rear;			// 尾指针
};

// 初始化循环队列
Status InitQueue(SqQueue &Q)
{
	Q.base = new QElemType[MAXQSIZE];	// 分配内存空间
	if (!Q.base)
	{
		exit(OVERFLOW);
	}
	Q.front = Q.rear = 0;

	return OK;
}

// 获取循环队列的长度
int GetQueueLength(SqQueue Q)
{
	return (Q.rear - Q.front + MAXQSIZE) % MAXQSIZE;
}

// 循环队列入队
Status EntryQueue(SqQueue &Q,QElemType e)
{
	if ((Q.rear + 1) % MAXQSIZE == Q.front)
	{
		return ERROR;		// 循环队列已满
	}

	Q.base[Q.rear] = e;
	Q.rear = (Q.rear + 1) % MAXQSIZE;	// 尾指针+1
	return OK;
}

// 循环队列出队
Status OutputQueue(SqQueue& Q, QElemType& e)
{
	if (Q.rear == Q.front)
	{
		return ERROR;		// 循环队列为空
	}

	e = Q.base[Q.front];
	Q.front = (Q.front + 1) % MAXQSIZE;	// 头指针+1

	return OK;
}

// 获取循环队列的第一个元素
SElemType GetHeadQueue(SqQueue Q)
{
	if (Q.front != Q.rear)
	{
		return Q.base[Q.front];		// 返回循环队列的第一个元素
	}
}


int main()
{
	int choose, flag = 0;
	SqQueue Q;
	QElemType e, j;

	cout << " 1.队列初始化"<< endl;			
	cout << " 2.入队" << endl;
	cout << " 3.出队" << endl;
	cout << " 4.获取第一个元素" << endl;
	cout << " 0.退出" << endl;

	choose = -1;
	while (choose != 0)
	{
		cout << "请选择循环队列的操作项【0-4】：";
		cin >> choose;
		switch (choose)
		{
		case 1:
			if (InitQueue(Q))
			{
				flag = 1;
				cout << "循环队列初始化成功" << endl;
			}
			else
			{
				cout << "循环队列初始化失败" << endl;
			}
			break;
		case 2:
		{
			fstream file;
			file.open("Queue.txt");
			if (!file)
			{
				cout << "文件打开失败" << endl;
				return ERROR;
			}

			if (flag)
			{
				flag = 1;
				cout << "循环队列入队元素依次为：" << endl;
				while (!file.eof())
				{
					file >> j;
					if (file.fail())
					{
						break;
					}
					else
					{
						EntryQueue(Q, j);
						cout << j << " ";
					}
				}
				cout << endl;
			}
			else
			{
				cout << "循环队列未创建" << endl;
			}
			file.close();
		}
		break;

		case 3:
			cout << "循环队列依次出队的元素为：" << endl;
			while (OutputQueue(Q,e))
			{
				flag = -1;
				cout << e << " ";
				
			}
			cout << endl;
			break;
		case 4:
			if (flag != -1 && flag != 0)
			{
				cout << "循环队列的第一个元素为：" << GetHeadQueue(Q) << endl;
			}
			else
			{
				cout << "队列中无元素" << endl;
			}
			break;
		}

	}
	return 0;
}