在 c++e 中使用 do-while 循环进行密码检查时出现错误 "code will never execute"

Question

我在我的密码函数中加入了一个 do/while 循环，但它不起作用。我使用 xcode10 编写 C++ 代码，当我在 while 语句后使用分号时，它会显示一条错误消息，指出代码永远不会执行

string password (string g)
{
    string ch = "hello" ;
    cout << "Enter password";
    getline(cin, g);
    do {
        if (ch.compare(g) != 0) {
            cout << " INCORRECT PASSWORD";
            return (0);
        } else {
            cout << "correct password";
            return (string(g));
        }
    } while (ch.compare(g) == 0);  //this is where it shows the error that the code will never exec
}

我想加入这个循环和其他一些东西，这样我就可以让它成为一个无限循环，直到您输入正确的密码。

Answer 1

好吧，在你的 if 语句中，你将 return 在这两种情况下导致函数停止，因此它永远不会到达 while 条件来测试它

  string password(string g)
{
    string ch = "hello";
    cout << "Enter password\n";
    do
    {
        getline(cin, g);

        if (ch.compare(g) != 0)
        {
            cout << " INCORRECT PASSWORD\n";
        }
        else {
            cout << "correct password";
            return (string(g));
        }
    } while (ch.compare(g) != 0);  
}

Answer 2

在“if”和“else”中都有Return语句。您可以看到，无论 ch.compare(g) 的结果是什么，该函数都会 return 给它的调用者。

这就是它永远不会执行“while”的原因。

尝试在代码的不同位置设置 Return 语句 :)

Answer 3

如果 EOF.

，您还需要检查是否也收到了输入

string password() { // you don't need g as parameters in, your overwriting it
    string const ch = "hello"; // make ch const to show it not supposed to change
    cout << "Enter password";
    string g; // defining g here since now you need it
    while (getline(cin, g)) { // check that the read from cin is OK
        if (ch != g) { // simple notation for comparing two strings. There's also == available
            cout << "INCORRECT PASSWORD. Please try again\n"; // no return if you want to try again
        } else {
            cout << "correct password";
            return g; // you could also return ch here since they have the same content
        }
    }
    cout << "Unable to read line. aborting\n"; // not really a lot you can do if there is no input to read.
    return string(); // returning empty string.
}

在 c++e 中使用 do-while 循环进行密码检查时出现错误 "code will never execute"

Getting error "code will never execute" when using do-while loop for password checking function in c++e

c++

xcode

xcode10