Program:

The source code to demonstrate the validation of username and password is given below. The given program is compiled and executed successfully on Microsoft Visual Studio.

//C# program to demonstrate the validation of username and password.

using System;

class Demo
{
    public static int Main()
    {
        string username = "";
        string password = "";

        Console.Write("Enter Username(only 4 characters):");
        username = Console.ReadLine();

        Console.Write("Enter Password: (minimum 6 characters)");
        password = Console.ReadLine();

        if (username.Length != 4)
        {
            Console.WriteLine("Please enter correct username");
            return -1;
        }
        else if (password.Length < 6)
        {
            Console.WriteLine("Please enter correct password");
            return -1;
        }

        Console.WriteLine("Username: " + username);
        Console.WriteLine("Password: " + password);
        return 0;
    }
}

Output:

Enter Username(only 4 characters):abcd
Enter Password: (minimum 6 characters)Include@help
Username: abcd
Password: Include@help
Press any key to continue . . .

Explanation:

Here, we created a class Demo that contains the Main() method. The Main() method is the entry point for the program, here we created two string variables username and password. Then we read the value of the username and password. Here, we checked the length of user and password for validation, if entered username and password is correct then print them on the console screen otherwise print the error message on the console screen.