Question

我似乎无法弄清楚为什么get_password函数调用将始终返回qwert，无论我传入函数的字符串是什么。我的问题是我无法看到这个函数中的字符串比较出了什么问题。

string get(string askfor, int numchars, string input)
{
    cout << askfor << "(" << numchars << " characters): ";
    cin >> input;
    return input;
}

string get_password(string name)
{
    string pwd;
    if (name == "botting"){
        pwd = "123456";
    }
    else if (name == "ernesto") {
        pwd = "765432";
    }
    else if (name == "tong") {
        pwd = "234567";
    }
    else {
        pwd = "qwert";
    }

    return pwd;
}

int main()
{
    string name;
    string pwd;
    string passwd;
    cout << "Address of name =" << &name << "\n";
    cout << "Address of pwd =" << &pwd << "\n";
    cout << "Address of passwd =" << &passwd << "\n";

    bool authenticated = false;
    while (!authenticated)
    {
        // call one 
        string name1 = get("Name", 7, name);
        cout << "call one returned: " << name1 << endl;

        // call two
        string pass1 = get_password(name);
        cout << "call two returned: " << pass1 << endl;

        //call three
        string pass2 = get("Password", 7, passwd);
        cout << "call three returned: " << pass2 << endl;

        // compare the two passwords
        authenticated = false;
        if (pass1 == pass2) {
            cout << "Welcome " << name << "\n";
            authenticated = true;
        }
        else {
            cout << "Please try again\n";
        }
    }

    return 0;
}

Answer 1

将name1传递给第二个电话：

    // call one 
    string name1 = get("Name", 7, name);
    cout << "call one returned: " << name1 << endl;

    // call two
    string pass1 = get_password(name1); // change this variable
    cout << "call two returned: " << pass1 << endl;

get()将名称返回到name1字符串，并且不会更新name变量本身，因为此name仍为空字符串。

Answer 2

那是因为你永远不会分配name任何内容。它被初始化为""，并且永远不会改变。由于这与get_password中的所有案例都不匹配，因此它始终属于else案例，这会产生"qwert"。

我认为问题在于您的get函数会更好地编写如下：

string get(string askfor, int numchars)
{
    string input; // input shouldn't be an argument
    cout << askfor<<"("<<numchars<<" characters): ";
    cin >> input;
    return input;
}

您可以使用结果分配到name：

name = get("Name", 7);

Answer 3

您只需要通过参考而不是值。

string get(string askfor, int numchars, string &input)
{
    cout << askfor << "(" << numchars << " characters): ";
    cin >> input;
    return input;
}

比较函数调用返回的字符串

3 个答案: