照着老师的代码运行，居然是错的？！

代码

 $dir=dirname(__file__);

 require $dir."/phpexcel/phpexcel.php";

 $objPHPExcel=new PHPExcel();

 $objsheet=$objPhPExcel->getActiveSheet();//此行为第5行

 $objsheet->setTitle("demo");

 $objSheet->setcellValue("A1","姓名")->setCellValue("B1","分数");

 $objWriter=PHPExcel_IOFactory::createWriter($objPHPExcel,"Excel5");

 $objWriter->save("demo.xls");

错误提示：Notice: Undefined variable: objPhPExcel in D:\WWW\demo.php on line 5