Dynamically count fields in an internal table

The code was written in R/3 4.6c.

FUNCTION ZMANDY_EXCEL_UPLOAD.
*"----------------------------------------------------------------------
*"*"Local interface:
*"  IMPORTING
*"     REFERENCE(FILE_NAME) TYPE  RLGRAP-FILENAME DEFAULT
*"       'C:WINDOWSDESKTOP'
*"  TABLES
*"      INTERNAL_TAB
*"----------------------------------------------------------------------

INCLUDE OLE2INCL.

DATA: STR(20),NDATE(10).
DATA: ROW TYPE I VALUE 1, COL TYPE I VALUE 1.
DATA OBJ TYPE OLE2_OBJECT.
DATA WORKBOOK TYPE OLE2_OBJECT.
DATA SH TYPE OLE2_OBJECT.
DATA CELL TYPE OLE2_OBJECT.
DATA RANGE TYPE OLE2_OBJECT.
DATA APP TYPE OLE2_OBJECT.
DATA SEL TYPE OLE2_OBJECT.
DATA COLUMNS TYPE OLE2_OBJECT.
DATA TYP.
FIELD-SYMBOLS: <F>.

CREATE OBJECT OBJ 'excel.application'.
SET PROPERTY OF OBJ 'visible' = 1.
CALL METHOD OF OBJ 'Workbooks' = WORKBOOK.
WRITE :/ 'workbook', SY-SUBRC.
CALL METHOD OF WORKBOOK 'add'.
CALL METHOD OF OBJ 'Worksheets' = SH EXPORTING #1 = 1.
CALL METHOD OF SH 'Activate'.



LOOP AT INTERNAL_TAB.
COL = 1.
do.
ASSIGN COMPONENT SY-INDEX OF STRUCTURE INTERNAL_TAB TO <F>.
IF SY-SUBRC <> 0.
EXIT.
ENDIF.
DESCRIBE FIELD <F>. "TYPE TYP COMPONENTS N.
CALL METHOD OF SH 'Cells' = CELL EXPORTING #1  = ROW #2 = COL.
SET PROPERTY OF CELL 'value' = <F>. "VALUE.
*PERFORM INSTERDATA USING ROW COL <F>.
COL = COL + 1.
ENDDO.
ROW = ROW + 1.
ENDLOOP.
STR = ROW.
ENDFUNCTION.