C Collection of code snippets by Arne Vajhøj 
C (from articles on eksperten.dk / vajhoej.dk written sometime between 2004 and now) 
      PROGRAM SUB
      INTEGER*4 I
      DO 100 I=1,10
        CALL TESTFAC(I)
100   CONTINUE
      END
C
      SUBROUTINE TESTFAC(N)
      INTEGER*4 N
      INTEGER*4 FAC
      EXTERNAL FAC
      WRITE(*,*) N,FAC(N)
      RETURN
      END
C
      INTEGER*4 FUNCTION FAC(N)
      INTEGER*4 N
      INTEGER*4 RES,I
      RES=1
      DO 100 I=1,N
        RES=RES*I
100   CONTINUE
      FAC=RES
      RETURN
      END