How to use the arrow keys in a custom TI program

Question

I have looked at as many functions as I can and I still can't find one that lets you intercept the click of a TI arrow key click.

Answer 1

For Basic programs, which are run with the "Prog" button, you'll need to call getKey, which returns a key code for the last button pressed. The arrow buttons are mapped to codes 24, 25, 26, and 34.

More information is available at TI-Basic Developer, underneath the heading "Reading Keypresses".

Answer 2

I know this is an old question, but I think this point might still be relevant.

If you are using the key input to move a character, or shift a value somehow, you are almost always better off avoiding if-then-else statements.

The fastest method is usually to do something like this:

:getkey -> A
:X+(A=24) -> X
:X-(A=26) -> X
:Y+(A=25) -> Y
:Y-(A=34) -> Y

which can be further condensed to:

:getkey -> A
:X+(A=24)-(A=26) -> X
:Y+(A=25)-(A=34) -> Y

Instead of dealing with the logic through the if statements, we utilize the fact that the (A=24) has a 'boolean' (0 or 1) value. So we add or subtract 1 if it is a certain value.

Setting limits is also fairly easy:

:getkey -> A
:X+(A=26)(X<=20)-(A=24)(X>0) -> X
:Y+(A=25)(Y<=15)-(A=34)(Y>=3) -> Y

So if (X<20) it will multiply by 1, but when X>=20, (X<20) will multiply by 0, negating the incriment.

I use another technique to help with selecting values in some of my programs: The left and right keys increment and decrement a variable by a different value than the up and down keys do. However, it requires some more logic.

:getkey -> A
:X+10(A=26)(X+10<=100)-10(A=24)(X-10>=0) -> X
:Y+(A=25)(Y<15)-(A=34)(Y>3) -> B

In this case, the left and right arrows go by tens, and the up and down go by ones. (X+10<=100) is used instead of (X<100) because the latter will be true if X=99 so X can go up to 109. The former makes sure that adding ten will not exceed the limit.

Answer 3

You should be able to do it with the getkey command.

getkey (Store as) (Variable) A
while A=0
getkey (Store as) A

Then you can recall the variable A throughout the program. Each key has a number that is called through the getkey command. So you can use that variable by,

If A = 25
...
If A != 25
...

(25 would be the up arrow)