怎么做啊啊啊啊啊啊

没过！！！！！
啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊

#include <iostream>
#include <vector>
#include <string>
using namespace std;

int main() {
    int m;
    cin >> m;
    vector<string> history;
    int currentIndex = -1;
    bool canForward = false;

    for (int i = 0; i < m; ++i) {
        char op;
        cin >> op;
        if (op == 'v') {
            string url;
            cin >> url;
            history.resize(currentIndex + 1);
            history.push_back(url);
            currentIndex++;
            canForward = false;
            cout << url << endl;
        } else if (op == 'b') {
            if (currentIndex > 0) {
                currentIndex--;
                canForward = true;
                cout << history[currentIndex] << endl;
            } else {
                cout << "?" << endl;
            }
        } else if (op == 'f') {
            if (canForward && currentIndex + 1 < history.size()) {
                currentIndex++;
                canForward = false;
                cout << history[currentIndex] << endl;
            } else {
                cout << "?" << endl;
            }
        }
    }
    return 0;
}