ESQL C programming to create XLS file

Hi,

Iam getting an "-NaNQ" error on writing float values into xls.

/* Following is the query which gets the sum of 2 amounts (decimal values)from a table*/
sprintf(szSQLSelect,"Select case when (select sum(ac.amt1+ac.amt2) from "
                                 "Account_table ac ) <= 0 then 0.0000 else " 
                                " (select sum(ac.amt1+ac.amt2) from Account_table ac ) end actual");

/* the query is excuted and the actual amount is fetched into the float variable "factualamt" */
$double factualamt;
EXEC SQL FETCH POWeeklySelectStmt_c INTO :factualamt;

/* Now im writing that value into the xml file as follows */
    fprintf(gszReportFileName,"<Row> \n");
   if( fActualAmt != 0.0000  ){
 fprintf(gszReportFileName,"\t\t<Cell><Data ss:Type='Number'>%4lf</Data></Cell>\n <\Row>\n",  fActualAmt);
    }
     else{
    fprintf(gszReportFileName,"\t\t<Cell><Data ss:Type='Number'>%4lf</Data></Cell>\n <\Row>\n",  0.0000);
     }


Error:
But when i execute the program , i get an error while opening the xls saying that the data is an "-NaNQ"

Cause for error:
This error occurs whenever the amount value in the table is NULL.

Please help me with this issue

Regards
Devi