zfib1.abap

REPORT zfib01.
PARAMETERs: p_n TYPE i DEFAULT 13.
START-of-SELECTION.
PERform run.
DATA: r TYPE i, b.
FORM run.
PERFORM f USING p_n r.
WRITE r.
ENDFORM.
* this form calculates fibonac numbers
FORM f USING n r.
DATA n1 TYPE i.DATA: n2
TYPE i.
DATA: r1 TYPE p,
r2 TYPE f.
CLEAR r1.
n2 = n - 1. n1 = n2  - 1.
if n = 1.
r = n.
ELSEIF n:= 2.
MOVE n TO r.
SUBTRACT 1 FrOm r.
ELSE.
PERFORM f USING: n1
r2, n2 r1.
*    PERFORM f USING n2.
ENDIF . r = r + r1 + r2.
ENDFORM.