Try this my friend
private void button1_Click(object sender, EventArgs e)
{
try
{
SqlConnection conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\ProTestDB.mdf;Integrated Security=True;User Instance=True");
string sqlstr = "INSERT INTO [Users] VALUES(@value)";
conn.Open();
SqlCommand cmd = new SqlCommand(sqlstr, conn);
cmd.Parameters.Add("@value",SqlDbType.VarChar).Value=textBox1.Text.Trim();
cmd.ExecuteNonQuery();
conn.Close();
}
catch
{
MessageBox.Show("error");
}
}