Re: Fortran vs. C (was Re: Ken & Klaus.)

From: nessuno (nessuno_at_wigner.berkeley.edu)
Date: 09/20/04 

Date: 20 Sep 2004 11:50:01 -0700

beliavsky@aol.com wrote in message news:<3064b51d.0409180938.366bc3f2@posting.google.com>...
> nessuno@wigner.berkeley.edu (nessuno) wrote in message news:<f76c1166.0409170717.6ebe4e11@posting.google.com>...
> > Robert Newson <ReapNewsB@bullet3.fsnet.oc.ku> wrote in message news:<414ABB87.7070100@bullet3.fsnet.oc.ku>...
> > > Jeff Relf wrote:
> > >
> >
> > <snip>
> >
> > I did a lot of Fortran programming, most of it Fortran 66 (!). The
> > older Fortrans were pretty awful by today's standards of what a
> > programming language should be. One problem in upgrading them was
> > that you had to introduce incompatibilities with previous versions to
> > change some things. For example, on going from Fortran 66 to Fortran
> > 77, loop testing was moved to the start of the loop (in old Fortran,
> > all loops would execute at least once, unless you explicitly put in a
> > test to branch around them). I never learned Fortran 95, by then I
> > had switched to C. But it was obvious that in order to improve
> > Fortran 77, one would have to introduce further incompatibilities with
> > it.
>
> What seems "obvious" to you is incorrect in this case. Fortran 90
> greatly improved on Fortran 77 and maintained full backward
> compatibility. Every standard-conforming Fortran 77 program is an F90
> program, with the same meaning.
>
> > Once you've crossed this threshold, the question is, how far do
> > you go? If you're willing to go far enough in introducing
> > incompatibilities, you could transform Fortan exactly into C, maybe in
> > several steps if you wanted to do that. To me it seemed pointless.
> > Why not just use C?
>
> Because C is missing a lot of Fortran 95 features:
>
> (1) In Fortran 95, you can allocate a 3-D array with just
>
> real, allocatable :: x(:,:,:)
> allocate (x(n1,n2,n3))
>
> The correspoding C code is longer and trickier.
>
> (2) Passing arrays to functions is easier, since their size can
> queried. In Fortran you can just write
>
> call foo(x)
>
> and start subroutine foo with
>
> subroutine foo(x)
> real, intent(in) :: x(:,:,:)
> integer :: n1,n2,n3
> n1 = size(x,1)
> n2 = size(x,2)
> n3 = size(x,3)
>
> It's not easy to write a C function taking a general 2-D or 3-D array
> AFAIK.
>
> (3) Fortran 90/95 has array operations and array sections comparable
> to Matlab, letting you write fewer lines of code which better reflect
> the operations you are trying to perform.
>
> (4) When you do need loops, the Fortran DO-loop is safer than the for
> loop of C because you are guaranteed that the loop variable does not
> change within the loop. Usually this is what I want. If not, a
> DO-ENDDO loop without a loop variable but with an EXIT suffices.
>
> (5) Until C99, which is not so widely used as C90, there are no
> complex variables in C.

Yeah, I forgot to mention, original C didn't have complex variables,
and it would have hardly been difficult to have included them from the
beginning. And it's a pain to work around this.

Maybe if I had to do serious scientific programming again, I'd have to
learn Fortran 95, but I'm not enthusiastic about it.

Here is a question: Is there anything a general purpose programming
language (like C) needs that a scientific programming language doesn't
need? I don't think so, especially if you want to write large
programs. The converse is not true, of course, there are special
needs for scientific programs, like complex variables, and efficiency
is paramount. So in an ideal world, we'd have just one language for
both scientific programming and everything else.

Sounds like from what you have above that Fortran 95 passes length
arguments along with array pointers. Sort of like what PL/I used to
do with strings (they were called "dope vectors", i.e., the structures
containing the length and pointer to the actual string).

If Fortran 95 is backward compatible, then it keeps the record
oriented I/O, which I find very awkward after working with C.

Nessuno

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