Comments on: More calculators…

By: crit

crit — Sun, 13 Feb 2005 23:46:34 +0000

Ah yes, that numeric keypad thing is a bummer, which goes a long way to explaining why I can’t use the calculator at work that has all the numbers worn off the keys, thank you my friend. And hell, email me. It’s been far too long.

Oh yeah, three more things of note 1. I had lost your blog address (along with your email) so I googled you. Came up first hit. Gotta be happy with that, yeah? 2. watching the Sound of Music “what is it you cunt face?” thought of you 3. singing Brahms Deutsche Requiem with Choral Society with the inevitable memories of being surrounded by you, Pianezze, and $1.20…

XXX
crit
BTW - where’s your “email me” toggle???

By: medge

medge — Thu, 03 Feb 2005 11:24:33 +0000

Doesn’t your typical calculator keep a running result and not remember how it got there?
IE it would end up as:
(((2 * 2) + 2) * 2) = 12
And you have to implicitly tell it not to by using:
(2 * 2) + (2 * 2) = 8
I remember being involved in writing a JDO type thing that generates SQL on the fly, the brackets it used where quite interesting!
SO the lesson here is avoid ambiguity and learn to embrace the brace.

By: elwing

elwing — Wed, 02 Feb 2005 07:39:16 +0000

Just for yout information, I tried it on my Treo 650 calculator, and I get 12 in the standard mode, and 8 in “advanced” mode.

By: Chris

Chris — Wed, 02 Feb 2005 02:03:49 +0000

Of course Nat’s right - the rules of precedence are just that - rules. I guess it comes from my background in pure maths and physics that I just assume that all calculators work like the ones I have used all my life.

Not being a smalltalker myself I haven’t noticed that language’s precedence rules - but almost always I parenthesise (sp?) or refactor in my code - whatever the language - to make it absolutely clear.

Robert’s observation (in his blog) that mechanical calculators show running totals is an interesting one - and of course makes sense if you are always doing additions, as I guess is the standard user story for a mechanical calculator.

It does stick in my craw though, that a user of a mechanical style calculator has to write down the intermediate result to perform 2*2 + 2*2 - it seems really wierd to me.

I guess for a modern calculator, the question is more why don’t we show a paper trail in that case - make it explicit how the thing works. I’m sure I’ve seen that somewhere…

By: Anonymous

Anonymous — Wed, 02 Feb 2005 01:41:12 +0000

By the way, your spam filter is inaccurate. I could not write the word “s-p-e-c-i-a-l-i-s-e-d” (without the hyphens) because your filter didn’t like the sequence “c-i-a-l-i-s”.

It’s lucky you’re not writing about Scunthorpe.

By: Nat Pryce

Nat Pryce — Wed, 02 Feb 2005 01:39:41 +0000

Operator precedence is not a mathematical LAW, it’s a mathematical CONVENTION. There are lots of different methods of writing and evaluating expressions. E.g. Polish (used by LISP), Reverse Polish (Forth), etc. The method you don’t like is the same as used by several programming languages, including J and Smalltalk. The use of an evaluation convention is a trade-off between the advantages that the convention provides vs. the disadvantage of unfamiliarity to people who are used to what they learned in high-school maths.

I agree that a calculator aimed at the casual user should follow the most widely used convention. But even calculators don’t follow this rule when aimed at a specific markets — HP’s engineering calculators use RPN notation.

By: Liz

Liz — Wed, 02 Feb 2005 01:03:33 +0000

My Windows XP calculator doesn’t display the 6 in scientific mode - entries (display):
2 * (2)
2 + (4)
2 * (2)
2 = (8)
which is not quite as disturbing.

My Palm Tungsten T3 comes with an arithmetic logic calc. Its number keypad is arranged in the same way as a phone’s… not the same way as most numeric keypads. I guess this may be because they also produce the Handspring Treos, which are phones.

By: Robert Watkins

Robert Watkins — Wed, 02 Feb 2005 00:26:56 +0000

A rule of thumb, for me, would be that if it shows an interim result, then it should be an arithmetic logic calculator. The reason is simple: I could stop halfway through, come back, see the number, and proceed where I left off. Thus, the Windows XP calculator is “right” in the standard mode, and “wrong” in the scientific; it’s very disconcerting to see ‘6′ in the window, then multiply it by 2 to get ‘8′.

(As an aside: if you’re teaching students how to read equations, it’s better to give them arithmetic logic calculators; they can use the calculator to do the arithmetic while learning how to read the equation. Giving them the more powerful calculator hinders that)

The numeric keypad/ATM thing is easier to explain: two design decisions made at about the same time, when neither had much momentum. There was a 50/50 chance they would end up different. :)