Re: Help please with a small code conversion

From: Dave Seaman (dseaman_at_no.such.host)
Date: 10/19/04 

Date: Tue, 19 Oct 2004 19:17:12 +0000 (UTC)

On 19 Oct 2004 10:36:02 -0700, Jason wrote:
> I am trying to convert a piece of FORTRAN code to C++.

> write(ifile,*) h(i,j)

> Does this simply write to a file a entry from a Ith by Jth entry of a
> matrix?

Probably, but there's an outside chance that it could mean to call a
function named 'h' with arguments i and j. In Fortran you can't tell the
difference except by looking to see how (or whether) h is declared. If h
is not declared at all in that program unit, then it's a function.

>If so what does (ifile, *) do? Does this make the entry
> added to a file called (ifile)?

Not quite; ifile is an integer variable whose value is the unit number
associated with the file (sort of like file descriptors in C). The "*"
means that instead of specifying a format for the write, the program is
using "list directed output", which is somewhat similar in spirit to
using the "<<" output operator in C++, since the format is dictated by
the type of the item being written.

> Also there is another line that has me stuck

> implicit double precision(a-h,o-z)

The default specification in Fortran is

  implicit real (a-h,o-z)
  implicit integer (i-n)

which means you are allowed to have undeclared variables in Fortran, and
their types are inferred from the first letter of the name (hence the
saying: "God is REAL, unless declared INTEGER."). The purpose of the
implicit statement is to change the default type mapping.

> I am not sure the significance of implicit. How could I get the same
> effect using c++?

You can't. All variables must be given explicit types in C++. Think of
it as insurance againt typos. 

-- 
Dave Seaman
Judge Yohn's mistakes revealed in Mumia Abu-Jamal ruling.
<http://www.commoncouragepress.com/index.cfm?action=book&bookid=228>

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