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Question

好的，我现在已经学习了大约4天的C ++，这是我的第一个编程语言。所以这真正意味着我只有大约8个小时的编程经验，其中很多是阅读我的C ++书的介绍并弄清楚如何使用XCode。

无论如何，我的初学者C ++书要求我做以下事情：“写一个密码提示，只给用户一定数量的密码输入尝试，这样用户就不会轻易写出密码破解者。”

唯一的问题是我刚刚学会了循环，我认为这本书甚至没有涵盖如何限制尝试。有人可以帮忙吗？我见过this，但它对我来说太先进了，我不明白。这是代码:(真正基本的新代码...对不起，如果它侮辱你的情报）

#include <iostream>
#include <string>

using namespace std;

int main ()
{
string username;
string password;

while ( 1 )
{
    cout << "Enter your username: " << endl;
    cin >> username;
    cout << "Enter your password: " << endl;
    cin >> password;

    if ( username != "billy" && password != "bob" )
    {
        cout << "Incorrect username/password combination. Please try again." << "\n" <<
        endl;
    }

    else
    {
        break;
    }
}

cout << "Access granted." << endl;
}

Answer 1

while ( 1 ) { }构造重复{}内的任何内容到无穷大，除非你从循环中明确break。这是一个循环，顺便说一句。

经过多次尝试后，你怎么能打破它？你可以有一个计数器，它会随着每次尝试而增加，并在极限处从循环中断：

if ( ++counter >= limit )
    break;

或简单地在while内移动条件

while ( ++counter < limit )

或使用简单的for循环或do {} while()。

Answer 2

拿一些变量，比如tryCount，它记录了所做的尝试次数。将其初始化为0并在每次尝试失败时将其递增1。将条件置于while循环中，检查attemptCount是否小于允许的尝试次数（在下面的代码中取3）。所以，代码将是：

#include <iostream>
#include <string>

using namespace std;

int main ()
{
string username;
string password;
int attemptCount = 0;

while ( attemptCount < 3 )
{
cout << "Enter your username: " << endl;
cin >> username;
cout << "Enter your password: " << endl;
cin >> password;

if ( username != "billy" && password != "bob" )
{
    cout << "Incorrect username/password combination. Please try again." << "\n" <<
    endl;

    attemptCount++;
}

else
{
    break;
}
}

cout << "Access granted." << endl;
}

Answer 3

你的while(1)循环将永远继续，除非你还有一些计数器，你在每次尝试失败时都会增加。

但坦率地说......为什么有一个while循环和一个单独的计数器？您有一个已知的最大迭代次数;这是for循环的一种情况。

for (int attempts = 1; attempts <= 3; ++attempts) {
    ... get login info ...

    if (...username and password are correct...) {
        cout << "Access granted.\n";
        return 0;
    }
    else {
        cout << "Invalid login.\n";
    }
}

// Note as well, the default case (what happens if they make it through the loop)
// should be no access.  Otherwise, someone could just succeed by inputting three
// bad passwords.  :P
cout << "Too many invalid login attempts.\nExiting.\n";
return -1;

Answer 4

想想这是如何运作的：

#include <iostream>

using namespace std;
int main()
{
  const int MAXTRYS = 4;
  int numTrys = 0;

  while(numTrys != MAXTRYS)
  {
    cout << "Attempting login" << endl;
    ++numTrys;
  }
return 0;
}

Answer 5

您应该使用for循环，而不是while循环。有点像：

bool bSuccess = false;
for (int i = 0 ; i < maxAttemps ; ++i)
{
    // your stuff
    // set bSuccess = true when relevant
}

if (bSuccess)
{
    // ok, successfully logged in
}

无限循环通常仅限于无限循环（在退出之前永远等待网络消息等）。作为良好实践的经验法则，尽可能避免无限循环，break也会构造，因为它通常是一种hacky。要练习，你应该尝试编写一个很好的代码，转换成一个简单的数据流。

我猜你怀疑它，但这根本不安全（你在可执行文件的代码中用纯文本存储用户名和密码）。

Answer 6

我很难重新熟悉C ++，因为高中（@ 8年前）已经发生了很多变化，或者我的信息学老师很糟糕...... 我也发现“for”循环对于这种练习更好，但是“返回0”并不是真的。和“打破;”做同样的事？这就是我在这里看到的以及我已经“知道”的东西:)。像魅力一样。

#include <iostream>
#include <string>

using namespace std;
int main ()
{
int attempts = 0;
string password;

for (int attempts = 0; attempts < 5; ++attempts )
{
    cout << "enter your password! \n";
    cin >> password;
    ++attempts;
    if ( password == "boo123" )
    {
        cout << "granted!";
        return 0;
    }
    else
    {
        cout << "denied! \n";
    }
}

}

还有一件事：所有循环都是无限的'直到你“破碎”;它或“返回0;”它...

Answer 7

/*Write a password prompt that gives a user only a certain number of password entry attempts—
so that the user cannot easily write a password cracker*/

#include <iostream>
#include <string>
using namespace std;
int main ()
{
    string password;
    int x = 1;

    while (1)  //This creates an overall top level infinite loop
    {
        cout << "Input password here: ";
        cin >> password;

       if ( password == "teddy") //This sets the condition for success
       {
           cout << "Access Granted!!!!";
           break; //The break is applied here to stop the cycle after success is made
       }

       else if ( password != "teddy") //This sets the condition for failure

       {
       cout << "Wrong username/password" << "\n" << x << " " << "wrong attempts" << "\n";
       ++x;

       if ( x > 5 ) // This is the counter limit portion. Limit set to 5 attempts

       {
           break;
       }

       }

    }

}

Answer 8

#include <iostream>

using namespace std;

int main()
{
    string password;
    int pCounter = 0;
    cout << "Enter Password here: ";
    getline(cin, password);
    while(pCounter <= 4){
        if(password != "winner"){
            cout << "Count: " << pCounter << endl;
            cout << "Try again..wrong entry.." << endl;
            cout << "Enter Password here: ";
            getline(cin, password);
            ++pCounter;
                if((password != "winner") && (pCounter == 4)){
                    cout << "The End..No more tries!!" << endl;
                    break;
                }
        }

        else{
            cout << "Welcome In Bro" << endl;
            break;
        }
    }
    return 0;
}

Answer 9

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使用命名空间标准；

int main（）{ 字符串密码=“设置”； //声明密码字符串输入//声明一个字符串供以后输入

for (int attempt = 1; attempt <= 3; attempt++) {        //if you fail the password 3 times you get kicked out
    cout << "enter password " << flush;
    cin >> input;
    if (input == password) {                            //checks to make sure the user input matches set password
        cout << "granted";
        return 0;                                       //once correct password is put in the program ends
    }
    else {                                              //if password is wrong repeat till right or 3 trys
        cout << "you fail" << endl;
    }
}

}

限制C ++中的登录尝试

9 个答案:

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