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HP-35S 'Guide for Dummies' being posted online
05-03-2015, 11:12 AM
Post: #32
RE: HP-35S 'Guide for Dummies' being posted online
From 3. Introduction to RPN:
Quote:You discover the way to convert °F to °C is:

°C = (5/9) x (°F – 32)

You start with writing the numbers on the whiteboard:

9
5
72
32

But why did you chose this order? Why are 5 and 9 swapped?

Most probably because otherwise you'd have to use [x<>y] twice:

5
9
72
32
-
x<>y
/
x<>y
*


Given this example there are two possibilities I would calculate it.

Outside in:

5
9
/
72
32
-
*

This is basically how a computer translates the algebraic expression to RPN:
Code:
echo "(5 / 9)*(72 - 32)" | bc -c
 5 9/ 72 32-*ps.

Inside out:

72
32
-
5
9
/
*

In both cases there's no need to swap any values.

Quote:For good measure, let’s try the built-in calculator °F to °C function Smile

From a pedagogical point of view this devaluates your introduction to RPN. Why do something in a complicated way when there's a dedicated key for it?

Recommendation:
You propose to push all the numbers first and only then start with the calculations. But this won't work with more than 4 numbers. Instead you should explain why and when an intermediate result is kept on the stack for later use.

Given that there's a built-in function I think that this is a bad example. I'd probably use a grocery store problem like calculating the total of buying the multiple items you need for a cake.

Kind regards
Thomas
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RE: HP-35S 'Guide for Dummies' being posted online - Thomas Klemm - 05-03-2015 11:12 AM



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