我正在创建一个 c++ 程序，其中用户有 2 次尝试密码用户名组合的尝试。如果他们不能得到它，他们的程序就会停止

Question

这是我得到的错误。我刚刚从 python 转到 c++，这是一个巨大的调整。这是程序的描述：编写程序，使其创建 3 个或更多有效的用户名/密码组合，然后提示用户输入用户名和密码。如果组合有效，则打印确认消息。如果组合在第一次尝试时无效，则打印一条警告消息并让用户再试一次（再次提示他们输入用户名和密码）。如果第二次尝试正确，则打印确认消息。如果第二次尝试不正确，请打印一条指责消息。在任何一种情况下，在第二次尝试后停止程序。显示三种情况的输出：第一次尝试正确的用户名/密码；第二次尝试正确；两次尝试都不正确。

$ g++ username_password.cpp -o username_password
username_password.cpp: In function ‘int main()’:
username_password.cpp:34:2: error: ‘else’ without a previous ‘if’
  else if (username != "Veasy62" && username != "tveasy62" && username != "terriyon62" && password != "a65908" && password != "a1065908" && password != "Aa1065908");
  ^




#include <iostream>
#include <string>

using namespace std;

int main()

{

    int pswrd_attempts = 0;
    string username;
    string password;
    cout << "Enter your username: " << "\n";
    getline( cin, username, '\n' );
    cout << "Enter your password: " << "\n";
    getline( cin, password, '\n' );
    while (username != "Veasy62" && username != "tveasy62" && username != "terriyon62" && password != "a65908" && password != "a1065908" && password != "Aa1065908");
    {
        pswrd_attempts++;
        cout << "Enter your username: " << "\n";
        getline( cin, username, '\n' );
        cout << "Enter your password: " << "\n";
        getline( cin, password, '\n' );

        if (pswrd_attempts > 2)

        {
            cout << "You've ran out of attempts" << "\n";
        }

    }
    else if (username == "Veasy62" && username == "tveasy62" && username == "terriyon62" && password == "a65908" && password == "a1065908" && password == "Aa1065908");
    {
        cout << "Correct password!" << "\n";



    }





}

Answer 1

在定义while 语句的行的末尾有一个分号。这会造成各种破坏。

您报告的另一个问题是因为您的 else 子句超出了应该是 while 的范围，而不是附加到 if。

Answer 2

如果你检查你的 IF 语句，对应的 else 它在错误的块级别：

    if (pswrd_attempts > 2)
        {
            cout << "You've ran out of attempts" << "\n";
        }

}

    else if...

您需要将右括号移到 els if 块后面。

Answer 3

我相信这就是你想要达到的目标。

#include <iostream>
#include <string>
#include <vector>
#include <conio.h>

void printAttempts( unsigned attempts, const std::string& messageTryAgain, const std::string messageOutOfAttempts ) {
    if ( attempts == 0 ) {
        std::cout << messageTryAgain << std::endl;
    } else {
        std::cout << messageOutOfAttempts << std::endl;
    }
} // printAttempts

int main() {
    std::vector<std::string> vUserNames;
    std::vector<std::string> vPasswords;

    vUserNames.push_back( "username1" );
    vUserNames.push_back( "username2" );
    vUserNames.push_back( "username3" );

    vPasswords.push_back( "pass1" );
    vPasswords.push_back( "pass2" );
    vPasswords.push_back( "pass3" );

    unsigned passwordAttempts = 0;
    std::string username;
    std::string password;

    const std::string tryAgain( "You have 1 attempt remaining.\n" );
    const std::string outOfAttempts( "You are out of attempts.\n" );

    while ( passwordAttempts < 2 ) {
        std::cout << "Enter your username: " << "\n";
        getline( std::cin, username, '\n' );

        std::cout << "Enter your password: " << "\n";
        getline( std::cin, password, '\n' );

        bool usernameFound = false;
        bool passwordFound = false;

        for ( unsigned u = 0; u < vUserNames.size(); ++u ) {
            if ( username == vUserNames.at( u ) ) {
                usernameFound = true;
                continue;
            }
        }

        for ( unsigned p = 0; p < vPasswords.size(); ++p ) {
            if ( password == vPasswords.at( p ) ) {
                passwordFound = true;
                continue;
            }
        }

        if ( usernameFound && passwordFound ) {
            std::cout << "You have successfully entered a valid username(" << username << ") and password(" << password << ")" << std::endl;
            break; // Uncomment this line to check out all possible combinations; The loop will continue until you run out of attempts.

        } else if ( usernameFound && !passwordFound ) {
            std::cout << "You have entered a valid user name(" << username << ")" << std::endl
                      << "however, you have entered an invalid password(" << password << ")" << std::endl;
            printAttempts( passwordAttempts, tryAgain, outOfAttempts );

        } else if ( !usernameFound && passwordFound ) {
            std::cout << "You have entered an invalid username(" << username << ")" << std::endl
                      << "You did however entered a valid password(" << password << ")" << std::endl;
            printAttempts( passwordAttempts, tryAgain, outOfAttempts );

        } else {
            std::cout << "You have entered an invalid username(" << username << ") and password(" << password << ")" << std::endl;
            printAttempts( passwordAttempts, tryAgain, outOfAttempts );
        }
        passwordAttempts++;
    }

    std::cout << "\nPress any key to quit" << std::endl;
    _getch();

} // main

让我知道这对你有什么影响。