What I would like to do is write a program for my TI-85 that will turn it into a construction calculator (i.e. a calc that will add, subtract, multiply and divide feet and inches). The reason I am trying to do this is that in my job I often have to calculate the area of something with holes, notches, etc. that I need to subtract from the total area. For example, I need to be able to multiply 40 feet 6 1/2 inches by 11 feet 2 3/4 inches and then subtract 4 feet 7 inches multiplied by 4 feet 11 3/4 inches. Right now in order to do this I use a construction calculator and write down all the multiples, then manually type in the subtraction. With my TI, I could potentially do everything in one step. Here's the problem: even though I have had this calc for roughly 20 years, I have never learned to program on it. Can anyone suggest a place for me to get information on beginning TI-85 programming? Also, where would I start to write this program?

Welcome to Cemetech, it's good to have you here. I recall that you were on #ti talking about problems with using your linking software with your TI-85; have you been able to resolve it? If you get a chance, be sure to Introduce Yourself. As far as programming tutorials go, the majority are for the TI-83+/84+ calculators, but most of the skills cross over:

http://tifreakware.net/tutorials

I would suggest looking through the manual and other 85 Basic programs on http://ticalc.org.

That said I do own a TI-86 which is very similar and I can see if I can help you whip something together. One important difference between the 85 and 86 is the 86 properly follows the order of operations where the 85 does not.


P.S. I am the Jonimus that helped you with your linking question on IRC and cemetech has its own IRC channel on efnet #cemetech, which is linked via a bot to the chat box to the left.

Weird, you learn something every day. What operation ordering does it mix up?

To quote the TI-86 guidebook

There are other slight differences as well but that is the one I could find quickly.

Thanks to you both! I need to get a silverlink cable and then I will be back. I will definitely try out both websites and look through the manual too. I appreciate your suggestions; they have made me feel very welcome!

I think I actually like that second version that the TI-85 performs better. I can't tell you how many beginner TI-83+ programmers write the Quadratic Equation like this and don't understand what's wrong with it:


Code:

Ok, I'm a beginner...what's wrong with it?

The "/2A" part is what is wrong; it's dividing by 2, and then multiplying by A, not dividing by (2*a)

I always treat variables as (2a) unless it's explicitly (2)*(a); looking back it's probably why I kept failing math later on in my education.

Jazmyn, don't worry too much about that; we're just geeking out with EOS trivia here. Chances are that if a program like yours you won't run into this sort of thing. Getting back to your program, it seems to me that each time the user enters a value, you'll need to ask them to input two things, the feet and then the inches. You can store this as feet+(inches/12), I suppose, but I think you'll get fewer math and round-off errors if you store each value in a two-element list of [feet, inches]. Then again, while adding two such things is easy (this is pseudocode):


Code:
, I could see things like multiplication and division getting headache-y.

Why not store everything as inches, do the calculations, and convert back to feet and inches?

^^ This.

It's easy to convert inches to feet+inches. Pseudocode:
Code:

"int()" is a function that takes the integer part of the number inside, so (for example) int(1.25) = 1.

It's even easier to convert feet+inches to inches. More pseudocode:
Code:

Because I didn't have enough sleep slash coffee yesterday and wasn't thinking straight. Thanks, Souvik, that is indeed the obvious good solution both for simplicity and avoiding rounding problems.