REPORT  Z12_004                                                     .
DATA: BEGIN OF line,
        col1 TYPE i VALUE 11,
        col2 TYPE i VALUE 22,
        col3 TYPE i VALUE 33,
      END OF line.
DATA comp(5) TYPE c VALUE 'COL3'.
FIELD-SYMBOLS: <f1> TYPE ANY,
                          <f2> TYPE ANY,
                          <f3> TYPE ANY.
ASSIGN line TO <f1>.

ASSIGN comp TO <f2>.

DO 3 TIMES.

  ASSIGN COMPONENT sy-index OF STRUCTURE <f1> TO <f3>.

  WRITE <f3>.

ENDDO.

ASSIGN COMPONENT <f2> OF STRUCTURE <f1> TO <f3>.

WRITE / <f3>.