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Hex Value $AD
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getKey

Overview

Returns the key code for the current keystroke, or 0, if no key is pressed.

Availability: Token only available from within the Basic editor.

Syntax

getKey

Location

prgm, I/O, 7:getKey

Description

The getKey command returns the value of the last key pressed since the last time getKey was executed. Reading key presses with getKey allows a program to transfer control to the user, and you can combine getKey with other commands to create menus, movement, or whatever else you want.

Every key has a number assigned to it, except for ON (which is used for breaking out of programs). The numbering system consists of a row and column: the rows go from one to ten, starting at the top; and the columns go from one to six, starting from the left. You just put the row and column together to get the key's number — for example, the ENTER key is located in row 10, column 5, making its value 105. The arrow keys look like they would be numbered separately from the other keys, but they actually follow this pattern as well. See the key codes page for a picture of the key codes on the calculator.

The value of getKey is cleared every time you read from it, until a new key is pressed. For this reason, except in very rare cases, you do not want to use the value of getKey in an expression directly, but store it to a variable first. It is also common to use getKey inside of a Repeat loop, so that the program can wait for the user to press a key.

:Repeat Ans
:getKey
:End
:Ans→K

Advanced Uses

You can put getKey in the condition of a loop, to make the loop repeat until any key or a particular key is pressed by the user. The same thing can be done with conditionals as well. This is useful if you don't want to store getKey to a variable, but you still want to have the user press a key. This works because of the way 'true' and 'false' get interpreted in TI-Basic.

:Repeat max(getKey={24,25,26,34
:End

Unlike the other keys, the arrow and DEL keys can actually be held down, which will cause the key to keep being repeated until it is unpressed. This functionality is very useful in games where the user needs to repeatedly press a key to move or shoot, although it does completely disable the other keys from being able to be pressed (which is important in multiplayer games, where everybody must share the keys).

Sometimes your program may do something for several seconds without user input (say, playing an animation), then pause and wait for a key to be pressed. The problem is that if a key is pressed during the animation, the next getKey will return the value of that key, and any loop set up to wait for a key press will exit immediately. The solution is to run a "dummy" getKey just before the loop begins — its value won't be used for anything, and it will reset the value of getKey to 0. This can also be used to clear keypresses meant for loading programs from inside a shell.

Error Conditions

  • ERR:INVALID occurs if this statement is used outside a program.

See Also

Source: parts of this page were written by the following TI|BD contributors: basickevin, burr, DarkerLine, Edward H, GoVegan, iPhoenixOnTIBD, Myles_Zadok, Weregoose.

History

Calculator OS Version Description
TI-82 1.0 Added
Authors: Adrien Bertrand