关于#解答#的问题，如何解决？

Question

请解答一下
谢谢
（麻烦把代码发在评论区，谢谢）

oi.nks.edu.cn

px.lboj.com.cn

Answer 1

#include <iostream>  
#include <stack>
#include<string>

using namespace std;

int main()  
{
    stack<string> st1, st2;  
    string cmd;

    while (true)  
    {  
        getline(cin, cmd);

        if (cmd == "QUIT")  
        {  
            break;  
        }

        if (cmd.substr(0, 4) == "VISI" && cmd.substr(0, 6) == "VISIT ")  
        {  
            st1.push(cmd.substr(6));  
            cout << st1.top() << endl;  
        }

        else if (cmd == "BACK")  
        {  
            if (st1.empty())  
            {  
                cout << "Ignored" << endl;  
            }  
            else  
            {  
                st2.push(st1.top());  
                st1.pop();
                cout << st2.top() << endl;  
            }  
        }

        else if (cmd == "FORWARD")  
        {  
            if (st2.empty())  
            {  
                cout << "Ignored" << endl;  
            }  
            else  
            {  
                st2.push(st2.top());
                st2.pop();
                cout << st1.top() << endl;  
            }  
        }  
    }

    return 0;  
}