用c++编程：用两个栈实现队列

#include <iostream>
#include <stack>

using namespace std;

template <class T>
struct Myqueue{
    T front()
    {
        if(s2.size()==0)
        {
            if(s1.size()==0)
            {
                cout<<"队列为空"<<endl;
                return 0;
            }
            while(s1.size()>0)
            {
                s2.push(s1.top());
                s1.pop();    
            }
        }
        return s2.top();
    }

        void pop()
        {
                if(s1.size()==0 && s2.size()==0)
                {
                        cout<<"队列为空"<<endl;
                }
                while(s1.size()>0)
                {
                        s2.push(s1.top());
                        s1.pop();
                }
                s2.pop();
        }
        void push(T &t)
    {
        if(s1.size()==0)
        {
            while(s2.size()>0)
            {
                s1.push(s2.top());
                s2.pop();
            }
        }
        s1.push(t);
    }


    stack<T> s1;
    stack<T> s2;    
};


int main(void)
{
    Myqueue<int> myqueue;
    int flag;
    int num;
    int i=0;
    for(i=0;i<10;i++)
        myqueue.push(i);
    for(i=0;i<10;i++)
    {
        cout<<myqueue.front()<<" ";
        myqueue.pop();
    }
    cout<<endl;
    while(1)
    {
        cout<<"请输入要执行的操作，入队或者出队,1为入队，2
为出队，3为打印队头,0为退出"<<endl;
        cin>>flag;
        if(flag==1)
        {
            cout<<"请输入要增加的结点的值"<<endl;
            cin>>num;
            myqueue.push(num);
        }
        else if(flag==2)
        {
            myqueue.pop();
        }
        else if(flag==3)
            cout<<"队头结点为："<<myqueue.front()<<endl;
        else 
            break;
    }
    return 0;
}