private void buttonLogin_Click(object sender, EventArgs e) { MY_DB db = new MY_DB(); SqlDataAdapter adapter = new SqlDataAdapter(); DataTable table = new DataTable(); SqlCommand command = new SqlCommand("SELECT * FROM users WHERE username = @usn AND password = @pass", db.getConnection); command.Parameters.Add("@usn", SqlDbType.VarChar).Value = textBoxUsername.Text; command.Parameters.Add("@pass", SqlDbType.VarChar).Value = textBoxPassword.Text; adapter.SelectCommand = command; adapter.Fill(table); if (table.Rows.Count > 0) { this.DialogResult = DialogResult.OK; } else { MessageBox.Show("Invalid username/password.", "Login Error", MessageBoxButtons.OK, MessageBoxIcon.Error); } }