c# - How to Eliminate Checking of Null Value Datatable in IF condition -


in page fetching value database & filling values in datatable. comparing values mac string in if. based upon condition in query there no records fetched, stuck in if condition , throws no row @ position 0 exception rather going else part.

my code is:

  string mac = getmac();         string qry = "select vuserid,password passtable vuserid='" + username.text + "' , flag='a'";         string qry = "select vuserid,password passtable flag='a'";         string strq = "select mac_id sysinfo appflag='a'";         using (sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["evalcon"].connectionstring))         {             try             {                  sqlcommand cmd = new sqlcommand(qry, conn);                 sqlcommand cmd1 = new sqlcommand(qry, conn);                 sqlcommand cmd2 = new sqlcommand(strq, conn);                 conn.open();                 sqldataadapter da = new sqldataadapter(cmd);                 sqldataadapter daa = new sqldataadapter(cmd1);                 sqldataadapter dap = new sqldataadapter(cmd2);                 datatable dt = new datatable();                 datatable dtt = new datatable();                 datatable tab = new datatable();                 da.fill(dt);                 daa.fill(dtt);                 dap.fill(tab);                 (int = 0; < tab.rows.count; i++)                 {                     (int x = 0; x <= dtt.rows.count - 1; x++)                     {                         if (mac == tab.rows[i]["mac_id"].tostring() || tab.rows.count != 0)                         {                             if (username.text == dtt.rows[x]["vuserid"].tostring() && password.text == dtt.rows[x]["password"].tostring())                             {                                 response.redirect("~/changepass.aspx");                                 break;                             }                             else                             {                                 lblmessage.visible = true;                                 lblmessage.forecolor = system.drawing.color.red;                                 lblmessage.text = "invalid username or password !!!";                              }                         }                         else                         {                             lblmessage.visible = true;                             lblmessage.forecolor = system.drawing.color.red;                             lblmessage.text = "invalid access point evaluation !!!";                         }                     }                 }              }                         {                 conn.close();                 conn.dispose();             }         }

first of all, may want give more meaningful names variables.

on side note, may want change loops foreach loop:

foreach (datarow tabrow in tab.rows.count) {     foreach (datarow dttrow in dtt.rows.count)     {         // logic here         // tab.rows[i]["mac_id"] becomes tabrow["mac_id"]         // ,         // dtt.rows[x]["vuserid"] becomes dttrow["vuserid"]         // , on...     } }

this way if there no records fetched won't go in.

after that, may want check conditions on rowcount > 0 datatables before going inside loops , act outside loop if rowcount 0.


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