static bool ValidatePassword(string password)
    {
        const int MIN_LENGTH = 8;
        const int MAX_LENGTH = 64;

        if (password == null) throw new ArgumentNullException();

        bool meetsLengthRequirements = password.Length >= MIN_LENGTH && password.Length <= MAX_LENGTH;
        bool hasUpperCaseLetter = false;
        bool hasLowerCaseLetter = false;
        bool hasDecimalDigit = false;

        if (meetsLengthRequirements)
        {
            foreach (char c in password)
            {
                if (char.IsUpper(c)) hasUpperCaseLetter = true;
                else if (char.IsLower(c)) hasLowerCaseLetter = true;
                else if (char.IsDigit(c)) hasDecimalDigit = true;
            }
        }

        bool isValid = meetsLengthRequirements
                    && hasUpperCaseLetter
                    && hasLowerCaseLetter
                    && hasDecimalDigit
                    ;
        return isValid;

    }


    bool IsValidEmail(string email)
    {
        try
        {
            var addr = new System.Net.Mail.MailAddress(email);
            return addr.Address == email;
        }
        catch
        {
            return false;
        }
    }


    private void bunifuFlatButton2_Click(object sender, EventArgs e)
    {
        Regex username = new Regex(@"^[a-zA-Z0-9]");

        if (textBox1.Text == "" || textBox2.Text == "" || textBox3.Text == "" || textBox4.Text == "")
        {
            System.Windows.Forms.MessageBox.Show("Fill out the required forms!");
            return;
        }
        else if (textBox2.Text != textBox3.Text)
        {
            System.Windows.Forms.MessageBox.Show("Your passwords are not matching");
        }

        else if ((ValidatePassword(textBox2.Text) == true) || (IsValidEmail(textBox4.Text) == true) || username.Match(textBox1.Text).Success)
        {
            using (SqlConnection connection = new SqlConnection(connectionstring I know works))
            {
                SqlCommand cmd = new SqlCommand("INSERT INTO tabl_login (username, password, email) VALUES (@username, @password, @email)");
                cmd.CommandType = CommandType.Text;
                cmd.Connection = connection;
                cmd.Parameters.AddWithValue("@username", textBox1.Text);
                cmd.Parameters.AddWithValue("@password", textBox2.Text);
                cmd.Parameters.AddWithValue("@email", textBox4.Text);
                connection.Open();
                cmd.ExecuteNonQuery();
            }

            MessageBox.Show("Congrats! You can sign in now!");
            Form2 objFrmMain = new Form2();
            this.Hide();
            objFrmMain.ShowDialog();
            this.Close();
        }