循環キューの実装

 ，head == tail ， 
#include<cstdlib>
#include<iostream>
#include<string>
using namespace std;
typedef struct node
{
     string key;
     string value;
     node *next;
}node;
#define LEN 20
typedef   int Elemtype;
class Queue
{
public:
       int head;
       int tail;
       int flag;
       Elemtype q[LEN];       
       Queue()
       {
              head = tail = 0;
              flag = 0;
              memset(q,-1,sizeof(q));
       }
       int enqueue(Elemtype e)
       {
           if( head == tail &&  flag == 1)
           {
                   cout << "queue full" << endl;
                   return -1;
           }
           q[tail] = e;
           tail = (tail + 1) % LEN;
           if(head == tail)flag = 1;
           return 0;
       }
       int dequeue(Elemtype &e)
       {
           if(head == tail && flag == 0)
           {
                   cout << "queue empty" << endl;
                   return -1;
           }
           e = q[head];
           head = (head + 1) % LEN;
           if(head == tail) flag = 0;
           return 0;
       }
};

int main()
{
    class Queue que;
    int i ;
    Elemtype elem;
    for(i = 0;i < 1000;i ++)
    {
          if(i % 3)
          {
               que.enqueue(i);
          }
          else 
          {
              int ret =  que.dequeue(elem);
              if(ret >= 0)cout << "i = " << i << " dequeue is :" << elem << endl;
          }
          system("pause");
    }

    return 0;
    }