rem: if (str[0] == 'q' || str[0] == 'Q')
add: if (str.empty() || str[0] == 'q' || str[0] == 'Q')
context: main(){    cout << "/////////////////////////////////////////////////////////\n\n";    cout << "\t\tA simple virtual machine...\n\n";    cout << "/////////////////////////////////////////////////////////\n\n";    cout << "Type an expression...or [q or Q] to quit\n\n";    vmachine    mach;       //  Our virtual machine    vector<int> code;       //  Our VM code    calculator  calc(code); //  Our parser    string str;    while (getline(cin, str))    {        if (str[0] == 'q' || str[0] == 'Q')            break;        code.clear();        if (compile(calc, str.c_str()))        {            mach.execute(&*code.begin());            cout << "\n\nresult = " << mach.top() << "\n\n";        }    }    cout << "Bye... :-) \n\n";    return 0;}