auto-genrate id using table

protected void generatedStudID()
    {
     
        cn = new SqlConnection(cs);
        cn.Open();
        int a=1;
        string k1 = "select * from patientreg where sno='" + a + "'";
        cm = new SqlCommand(k1, cn);
        dr = cm.ExecuteReader();
        if (dr.Read())
        {
            dr.Close();
            cm = new SqlCommand("select MAX(sno) from  TABLE", cn);
            int i = Convert.ToInt32(cm.ExecuteScalar());
            cn.Close();
            i++;
            Labelpid.Text = "PA-" + DateTime.Now.ToString("yyyy") + "-00-" + i.ToString();
            dr.Close();
        }
        else
        {
            dr.Close();
            Labelpid.Text = "PA-" + DateTime.Now.ToString("yyyy") + "-00-" + "1";

        }
        dr.Close();
        
          }