I've problems binding the values from the parsed Excel file to the DBI execute command. How exactly do I bind those values?

use strict;
use Spreadsheet::ParseExcel;
use Data::Dumper;

my $source_file = 'C:/mydocu~1/db/jokes.xls';

my $source_excel = new Spreadsheet::ParseExcel;
my $source_book = $source_excel->Parse($source_file);

my $dbh = do_connect();

my $sql = "INSERT INTO mytest VALUES(?,?,?,?);
my $sth = $dbh->prepare($sql);

# code lifted from a site...
my($iR, $iC, $oWkS, $oWkC);
foreach my $oWkS (@{$source_book->{Worksheet}}) {
   for(my $iR = $oWkS->{MinRow} ; 
      defined $oWkS->{MaxRow} && $iR <= $oWkS->{MaxRow} ; $iR++) {
      for(my $iC = $oWkS->{MinCol} ;
         defined $oWkS->{MaxCol} && $iC <= $oWkS->{MaxCol} ; $iC++) {
            $oWkC = $oWkS->{Cells}[$iR][$iC];
            print "( $iR , $iC ) =>", $oWkC->Value, "\n" if($oWkC);   
+         
      }
   }
}

# $sth->execute(var1, var2, var3, var4);
# I know the above line has to be somewhere in the foreach loop but I 
+just can't figure how :(
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