[Year 12 SofDev] Records and Arrays

Thu Aug 19 08:40:32 EST 2010

After a quick bit of research, the following approved languages do not follow the 'definition' of an array as stated on page 161 of the Fitzpatrick & Keane text:

Objective C
Python
Perl
Ruby
PHP
Visual Fox Pro

The other six language do. According to the definitions, the above languages do not have an 'array' type but are indeed following the definition for a 'record'. Despite the fact that for each of these languages the structures are described and explained as 'arrays' in their documentation and not referred to as 'record' types.

It would seem that Adrian's point of these definitions being used in the study design is important, and must be considered a requirement of the course. Equally, if you teach one of the languages above, your students are not going to understand this well without specific help, in my opinion, as this will not be their experience in practice.

The simple answer is that any language type that allows for multiple items to be referred to as part of a single variable, when the items are required to be of the same type you have an 'array' and when the items are allowed to be of differing types you have a 'record'. According to the study design but purely language dependent in real life.

Guy Flaherty
Xavier College

>>> "Adrian Janson" <janson.adrian.a at edumail.vic.gov.au> 18/08/10 05:58 PM >>> 
Hi Guy and all,

The definition of array and record are as you stated and I would have
thought that this was a common thing to all languages - but I am not
familiar with PHP at all - and was surprised to see that you could mix data
types in an array!  It is important to remember that it is in the study
design (and the next one to) and so is fair game for the examiners (even
though as you said - it would be possibly a controversial topic given the
way PHP treats arrays and records....)

Cheers,

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

Blog:  <http://jansona.edublogs.org/> http://jansona.edublogs.org

-----Original Message-----
From: sofdev-bounces at edulists.com.au [mailto:sofdev-bounces at edulists.com.au]
On Behalf Of Guy Flaherty
Sent: Wednesday, 18 August 2010 2:58 PM
To: sofdev at edulists.com.au
Subject: Re: [Year 12 SofDev] Records and Arrays

Laurie,

I initially thought exactly as you stated when I looked at the reference in
the book. So I did a quick search and in languages like c and pascal arrays
must be of the same data type and records(pascal)/struct(c) can have
different data types for items, as explained in the text.

Being a python using person myself, I am not used to this, as arrays can
have any type of data in them, and there really isn't a 'record' type in
python that I am aware of. I think php is similar.

It would seem that this kind of structure is language dependent, and so not
the best for an exam question, in my opinion.

Guy Flaherty

Xavier College 

>>> "Laurie Savage" <savage.john.l at edumail.vic.gov.au> 18/08/10 01:57 PM >>>

I have a problem. In Fitzpatrick and Keane p. 161 (and in the 2007 exam)

arrays and records are primarily differentiated by data type. So the text

says: "An array is an indexed collection of elements of the same type of

data"; "A ... record represents a group of different data elements".

But, in PHP, this works:

<?php 

$pizzaToppings = array('onion', 'tomato', 'cheese', 'anchovies', 'ham',

'pepperoni', 1.6, 200); 

echo "<h1>We like $pizzaToppings[5] PIZZA!</h1>";

$num = $pizzaToppings[6] * $pizzaToppings[7];

echo $num;

?>

i.e. the array is storing data of different types and not storing the

numeric data as a string. What am I missing here? I've done a search, but

these are the only references I've seen that define this as the main

difference. I've been labouring under the delusion that an array lives in

volatile memory and disappears once the application halts or reinitialises

and a record is written to disk. I know from the web that I'm not alone

here.

Laurie Savage

Pascoe Vale Girls College

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