c# - Export to csv has Object reference not set to an instance of an object -

i'm trying export sql server csv file query.

i'm getting error object reference not set instance of object on line

foreach (datacolumn dc in dt.columns) { } 

here code running this.

private datatable getdata() {     sqlconnection sqlcon = new sqlconnection("...");     sqlcommand sqlcmd = new sqlcommand();     sqlcmd.commandtext = "select top 10 * products.products";     sqlcmd.connection = sqlcon;      sqlcon.open();     sqlcmd.executescalar();     sqlcon.close();     return dt; }  protected void button3_click(object sender, eventargs e) {     datatable dt = getdata();      string attachment = "attachment; filename=datatable.xls";      response.clearcontent();     response.addheader("content-disposition", attachment);     response.contenttype = "application/vnd.ms-excel";      string tab = "";     foreach (datacolumn dc in dt.columns)     {         response.write(tab + dc.columnname);         tab = "\t";     }      response.write("\n");      foreach (datarow dr in dt.rows)     {         tab = "";          (int = 0; < dt.columns.count; i++)         {             response.write(tab + dr[i].tostring());             tab = "\t";         }          response.write("\n");     }      response.end(); } 

i'm not sure do.

you have fill datatable something:

private datatable getdata() {     datatable dt = new datatable();      sqlconnection sqlcon = new sqlconnection("...");     sqlcommand sqlcmd = new sqlcommand();     sqlcmd.commandtext = "select top 10 * products.products";     sqlcmd.connection = sqlcon;      sqlcon.open();     dt.load(sqlcmd.executereader());     sqlcon.close();      return dt; }