SqlDataAdapter s = new SqlDataAdapter(query, con); DataTable

namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}

private void button2_Click(object sender, EventArgs e)
{
this.Close();
}

private void button1_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\vukst\Documents\users.mdf;Integrated Security=True;Connect Timeout=30;");
string query = "Select Count(*) from ltbl Username = '" + textBox1.Text.Trim() + "' and Password = '" + textBox2.Text.Trim() + " ' ";
SqlDataAdapter s = new SqlDataAdapter(query, con);
DataTable ltbl = new DataTable();
s.Fill(ltbl);
if (ltbl.Rows.Count == 1)
{

this.Hide();

Form2 ss = new Form2();
ss.Show();
}
else
{
MessageBox.Show("Please check your username and password");
}
}
private void textBox1_TextChanged(object sender, EventArgs e)
{

}
}
}