c# program

//this is LoginForm
namespace PhoneBook
{
    public partial class LoginForm : Form
    {
        public LoginForm()
        {
            InitializeComponent();
        }
        SqlConnection connect = new SqlConnection("Data Source=DESKTOP-58TQHKQ;Initial Catalog=phonebook;Integrated Security=True");

        public void login()
        {
            using (SqlCommand commander = new SqlCommand("SELECT COUNT(*) FROM table_login WHERE username = @username AND password = @password", connect))
            {
                try
                {
                    connect.Open();

                    commander.Parameters.AddWithValue("username", txt_username.Text);
                    commander.Parameters.AddWithValue("password", txt_password.Text);

                    int result = (int)commander.ExecuteScalar();

                    if (result > 0 )
                    {
                        MessageBox.Show("Login is Successfull");
                        this.Hide();
                        PhoneBookMainFrm frm1 = new PhoneBookMainFrm();
                        frm1.Show();
                    }
                    else
                    {
                        MessageBox.Show("Invalid username or password");
                    }
                }
                catch(Exception ex)
                {
                    MessageBox.Show("Unexpected Error" + ex.Message);
                }
                finally
                {
                    connect.Close();
                }
            }
        }

        private void btn_login_Click(object sender, EventArgs e)
        {
            login();
        }
    }
}


// this is PhoneBookMainForm

namespace PhoneBook
{
    public partial class PhoneBookMainFrm : Form
    {
        public PhoneBookMainFrm()
        {
            InitializeComponent();
        }

        SqlConnection connect = new SqlConnection("Data Source=DESKTOP-58TQHKQ;Initial Catalog=phonebook;Integrated Security=True; MultipleActiveResultSets=True");


        public void necessary_ending_dbactions()
        {
            connect.Close();
            listviewdatabase.Items.Clear();
            txt_id.Text = "";
            txt_name.Text = "";
            txt_surname.Text = "";
            txt_phonenumber.Text = "";
            database_display();
        }

        public void database_display()
        {
            connect.Open();
            listviewdatabase.Items.Clear();

            using (SqlCommand db_displayer = new SqlCommand("SELECT *FROM phone_table", connect))
            {

                SqlDataReader reader = db_displayer.ExecuteReader();

                var items = new List<ListViewItem>();

                while (reader.Read())
                {
                    ListViewItem adder = new ListViewItem(reader["id"].ToString());
                    adder.SubItems.Add(reader["name"].ToString());
                    adder.SubItems.Add(reader["surname"].ToString());
                    adder.SubItems.Add(reader["phonenumber"].ToString());
                    items.Add(adder);
                }

                listviewdatabase.Items.AddRange(items.ToArray());

            }
            connect.Close();

        }

        public void database_save()
        {
            using (SqlCommand db_saver = new SqlCommand("INSERT INTO phone_table (id,name,surname,phonenumber) values (@id,@name,@surname,@phonenumber)", connect))
            {
                connect.Open();




                db_saver.Parameters.AddWithValue("@id", txt_id.Text);
                db_saver.Parameters.AddWithValue("@name", txt_name.Text);
                db_saver.Parameters.AddWithValue("@surname", txt_surname.Text);
                db_saver.Parameters.AddWithValue("@phonenumber", txt_phonenumber.Text);
                db_saver.ExecuteNonQuery();
            }
            connect.Close();
            necessary_ending_dbactions();
        }

        public void database_update()
        {


            String query = "UPDATE phone_table SET id=@id, name=@name, surname=@surname, phonenumber=@phonenumber WHERE id=@id";

            using (SqlCommand db_updater = new SqlCommand(query, connect))
            {
                db_updater.Parameters.Clear();

                db_updater.Parameters.AddWithValue("@id", txt_id.Text);
                db_updater.Parameters.AddWithValue("@name", txt_name.Text);
                db_updater.Parameters.AddWithValue("@surname", txt_surname.Text);
                db_updater.Parameters.AddWithValue("@phonenumber",txt_phonenumber.Text);

                connect.Open();

                db_updater.ExecuteNonQuery();
            }
            necessary_ending_dbactions();
        }

        public void database_delete()
        {
            connect.Open();

            using (SqlCommand eraser = new SqlCommand("DELETE FROM phone_table WHERE id=@id and name=@name and surname=@surname and phonenumber=@phonenumber",connect))
            {
                eraser.Parameters.AddWithValue("@id", txt_id.Text);
                eraser.Parameters.AddWithValue("@name", txt_name.Text);
                eraser.Parameters.AddWithValue("@surname", txt_surname.Text);
                eraser.Parameters.AddWithValue("@phonenumber", txt_phonenumber.Text);
                eraser.ExecuteNonQuery();

            }
            necessary_ending_dbactions();
        }

        private void button_display_Click(object sender, EventArgs e)
        {
            database_display();
        }

        private void button_save_Click(object sender, EventArgs e)
        {
            database_save();
        }

        private void listviewdatabase_MouseClick(object sender, MouseEventArgs e)
        {
            txt_id.Text = listviewdatabase.SelectedItems[0].SubItems[0].Text;
            txt_name.Text = listviewdatabase.SelectedItems[0].SubItems[1].Text;
            txt_surname.Text = listviewdatabase.SelectedItems[0].SubItems[2].Text;
            txt_phonenumber.Text = listviewdatabase.SelectedItems[0].SubItems[3].Text;
        }

        private void button_update_Click(object sender, EventArgs e)
        {
            database_update();
        }

        private void button_delete_Click(object sender, EventArgs e)
        {
            database_delete();
        }

        private void menu_exit_Click(object sender, EventArgs e)
        {
            if (MessageBox.Show("Are you sure ? ", "Exit", MessageBoxButtons.OKCancel) == DialogResult.OK)
            {
                Application.Exit();
            }
        }
    }
}