using System;

​

public class Program

{

    static void Main(string[] args)

    {

        string[,] userCredentials = new string[,]

        {

            {"user1", "password1", "De Guzman"},

            {"user2", "password2", "Dela Cruz"},

            {"user3", "password3", "Del Pilar"},

        };

​

        Console.Write("Enter username: ");

        string inputUsername = Console.ReadLine();

        Console.Write("Enter password: ");

        string inputPassword = Console.ReadLine();

        string userLastName = "";

        bool loginSuccess = false;

​

        for (int i = 0; i < userCredentials.GetLength(0); i++)

        {

            if (userCredentials[i, 0] == inputUsername && userCredentials[i, 1] == inputPassword)

            {

                loginSuccess = true;

                userLastName = userCredentials[i, 2];

                break;

            }

        }

​

        if (loginSuccess)

        {

            Console.WriteLine($"Login Successful, Welcome {userLastName}!");

        }

        else

        {

            Console.WriteLine("Invalid username or password.");

            return;

        }

​

        while (true)

        {

            Console.WriteLine();

            Console.WriteLine("1. Update Password");

            Console.WriteLine("2. Binary Search");

            Console.WriteLine("3. Log out");

            Console.Write("Enter your choice: ");

            string option = Console.ReadLine();

​

            if (option == "1")

            {

                Console.Write("Enter new password: ");

                string newPassword = Console.ReadLine();

                Console.WriteLine("Password updated!");

​

                for (int j = 0; j < userCredentials.GetLength(0); j++)

                {

                    if (userCredentials[j, 0] == inputUsername)

                    {

                        userCredentials[j, 1] = newPassword;

                        break;

                    }

                }

            }

            else if (option == "2") 

            {

                Console.Write("Binary Search");

                int[] arr = { 25, 31, 82, 57, 15,66,94 };

                int target = 66;

                int index = BinarySearch(arr, target);

                if (index != -1) {

                    Console.WriteLine($"Index of {target} in the array is: {index}");

                } else {

                    Console.WriteLine($"{target} not found in the array.");

                }

            }

            else if (option == "3")

            {

                Console.WriteLine("Logged out");

                break; 

            }

            else

            {

                Console.WriteLine("Invalid option.");

            }

        }

    }

​

    static int BinarySearch(int[] numbers, int target)

    {

        int left = 0;

        int right = numbers.Length - 1;

​

        while (left <= right)

        {

            int mid = left + (right - left) / 2;

​

            if (numbers[mid] == target)

            {

                return mid;

            }

            else if (numbers[mid] < target)

            {

                left = mid + 1;

            }

            else

            {

                right = mid - 1;

            }

        }

        return -1; 

    }

}