C # export DataTable data to an Excel table

Public Fileresult getexcelfile ()
        {
if (session["begindate"]! = NULL)
            {
string bdate = session["Begindate"]. ToString ();
DateTime ld = Convert.todatetime (session["Lastdate"]. ToString ());
DateTime ldate = ld. AddDays (1);
string lldate = Ldate. ToString ("Yyyy-mm-dd");
int ptkey = Convert.ToInt32 (session["process_ptr"]);
string procesql = "SELECT * from assay_process where rkey=" +ptkey;
DataTable Procedt = sqlhelper.querytable (procesql);
idataparameter[] Idatatitle = new Sqlparameter[3];
idatatitle[0] = new SqlParameter ("@BeginDate", bdate);
idatatitle[1] = new SqlParameter ("@LastDate", lldate);
idatatitle[2] = new SqlParameter ("@RKEY", Ptkey);
DataSet dttitle = Sqlhelper.runproceduresbyparameter ("Pro_getassalyinfobyexportprint", idatatitle);
DataTable dt = dttitle.tables[0];
string outstr = excelexport.outexcel (dt);
byte[] filecontents = Encoding.UTF8.GetBytes (outstr.tostring ());
return File (filecontents, "Application/ms-excel", "" "+ procedt.rows[0][" ProcessName "]. ToString (). Trim () + "Test document (" + bdate. Trim () + "-" + lldate. Trim () + "). xls");
            }
Else
            {
string qua_no = session["Quano"]. ToString ();
idataparameter[] Idatatitle = new sqlparameter[1];
idatatitle[0] = new SqlParameter ("@Qua_no", qua_no);
DataSet dttitle = Sqlhelper.runproceduresbyparameter ("Pro_getassalyinfobyqua_no", idatatitle);
DataTable dt = dttitle.tables[0];
string outstr = excelexport.outexcel (dt);
byte[] filecontents = Encoding.UTF8.GetBytes (outstr.tostring ());
return File (filecontents, "Application/ms-excel", "Lab document" + Qua_no. Trim () + "). xls");
            }
        }

C # export DataTable data to an Excel table