user input and password

Change your code to:

namespace trial
{
    public class Password
    {
        static void Main(string[] args)
        {
            Console.Write("Enter a username:  ");
            string username = Console.ReadLine();

            Console.Write("Enter a password:  ");
            string pass = Console.ReadLine();

            do
            {
                if (username == "john" && pass == "mjamaa")
                    Console.WriteLine("Login Error");

            }
            while (username == "john" && pass == "mjamaa");
            Console.WriteLine("Login successful");
        }
    }
}

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Regards, http://ift.tt/1e8mnao