[Year 12 SofDev] Records and Arrays

Thu Aug 19 23:01:23 EST 2010

Kevork,

Wikipedia states that the index for an array is an integer based one and
provides references from Donald Knuth and Paul E. Black to support this.
It states that this index is required to be used when calculating the
address of the memory location for each item in the array. This actually
is explained to be one of the general differentiators between an array
and a record, in that an array's memory addresses can be computed at
run-time using the integer index and a record's cannot be easily
computed at run-time.

I think it would be a brave list to argue against Knuth ;) I am not sure
if I am helping anyone here :D

Guy Flaherty

>>> "Kevork Krozian"  19/08/10 10:05 PM >>>
Hi Folks,

 Just watching from the sidelines at present and having a feeling of déjà
vu. There are quite a few examples of definitions that have
disadvantaged my
students in the past not least in the role and functions of  networking
components (hubs vs switches, modems and routers and firewalls and virus
protection etc )  as well as data types in programming definitions. 

The last time I used Pascal was around 1995 or so at least in so far as
programming at Year 12.

Sure I used records of files but more commonly found records as a single
line in a database which we are not allowed to use in our programming. I
haven't heard of a file of records for many years - only a database of
records. Perhaps, I will leave that discussion for another time.

More generally and this is related to the definition used by Adrian here
,
the index for an array does not have to be an integer. It can be any
enumerated type eg. Inbuilt ones such as characters defined by say the
ASCII
sequence, meaning 'a' , 'b' , 'c' ,'d' etc can be used to index an array
or
a user defined enumerated range eg. 'Jan', 'Feb' , 'Mar', 'Apr' etc can
also
be used to index an array.

I also come from the Fortran, Pascal, Cobol, C, Prolog, Java, PHP,
Python,
Visual C# pathway in my programming development and have had to make the
transition into new areas of programming where the older definitions are
no
longer uniformly found in all languages. That would be the evolution of
programming and the blurring of the definitions of data types akin to
the
analogy of applications that blur the lines that used to separate them (
think Word Processors, spreadsheets and databases).

Take Care

Kevork Krozian

Edulists Creator Administrator

www.edulists.com.au

tel: 0419 356 034

From: sofdev-bounces at edulists.com.au
[mailto:sofdev-bounces at edulists.com.au]
On Behalf Of Janson, Adrian A
Sent: Thursday, 19 August 2010 8:54 PM
To: Year 12 Software Development Teachers' Mailing List
Subject: Re: [Year 12 SofDev] Records and Arrays

Hi everyone,

I know that some of you were happy with the definitions I posted before,
and
I do want to keep them simple - but, how about this:

One-Dimensional Arrays

A one dimensional (or 1D) array is a data structure in which variables
are
grouped together under the same name and accessed via a number known as
the
'index'.  Although an array typically contains only one data type, it
can
consist of multiple data types (as is possible in some languages such as
PHP
and Python).

....

Records

A record is a structure that can be used to group together variables for
a
particular purpose.  Records are similar to arrays but whereas an array
usually contains elements all of the same type, the variables within a
record are usually of different types and sizes.  Indexing the elements
of a
record is often done via an identifier which is declared at the same
time as
the record.

The important thing - as some have stated already, is for us to be able
to
tell students: 'this is the standard definition of an array and a
record'.
So if a student were asked on the exam 'what is an array', they could
answer
'an array is a data structure in
which variables are grouped together
under
the same name and accessing using an index number'. - and get full
marks.

Adrian

Adrian Janson B.Sc, Dip.Ed, M.Ed
Director of ICT
Melbourne High School, Forrest Hill, South Yarra, Victoria 3141
Australia.
Phone: 03 9826 0711 International: +61 3 9826 0711
Fax: 03 9826 8767 International: +61 3 9826 8767
E-mail: janson.adrian.a at edumail.vic.gov.au

Website: http://www.mhs.vic.edu.au  

Blog: http://jansona.edublogs.org  

  _____  

From: sofdev-bounces at edulists.com.au on behalf of David Dawson
Sent: Thu 19/08/2010 8:46 PM
To: sofdev at edulists.com.au
Subject: Re: [Year 12 SofDev] Records and Arrays

What a fascinating discussion this is! (No I mean it!)
When I started teaching Pascal in 1998 - I was so confused by "records"
- and came to see them as "customised data types" and - having just
learnt some Java and C++ - I figured they were really like Classes - or
even objects.
In any case I have not come up against this mysterious "data structure"
in the other languages I have explored - in C they are constructed and
can be called anything - and I bet that the library file could be
renamed ""list_o_stuff" - even in Pascal.
I prefer PHP at present and in PHP - like so many languages - the thing
people seem to miss is that in "weakly typed languages" everything just
starts as a String and is dealt with "contextually" as someone cleverly
pointed out earlier. If there are numbers we wish to multiply the
language figures this out by our operations - very smooth!
An array is a list defined by a computer language to store temporary
Strings! Some languages limit these - if they insist on strong variable
typing.
I really hope records are just amended out of any reference in the study
design.
IMHO they died 10 years ago!

David Dawson
Head of Information Technology Learning Area
Head of Learning Technologies
St Kilda Rd Campus
Wesley College
577 St Kilda Rd
Melbourne 3004
Ph 8102 6340
Mob 0425 718147

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