Commodore Plus 4 - Page 182

170 Some Programming Techniques
Use CHR$ codes in the definition to use quotation marks or a key such as
a return or the ESCape key.
STEP 3 Verify the new definition by issuing a KEY command, which displays
a list of current key definitions.
Examples: KEY 1//INPUT//+CHR$(34) Displays INPUT".
KEY 6/TIST"+CHR$(13)+mUN"+CHR$(13) Issues a LIST command
and a RUN command.
RUN executes as soon as
the program is listed.
KEY 3,CHR$(27)+"TLIST"+CHR$( 13) Creates a screen window,
whose top left corner is
the current cursor loca
tion and whose bottom is
the lower right corner of
the screen. After the
window is set, a LIST
command is issued.
Calling a Function Key During Program Execution
The function key definition procedure for defining keys in immediate mode can
also be used in a program. INPUT can be used to accept function key definitions.
Of course, the input must end with a RETURN character from the definition or
the keyboard. GETKEY receives only the first letter of the definition. Also, if
GETKEY is called a second time following the receipt of a multiple character
function key definition, an error results.
To be able to use a function key in a GETKEY command, you must first
redefine the key as a single CHR$ code. This definition allows BASIC to consider
the function key to be a single key, not a string of characters. Once the key is
defined as a single key, you can press the key as input for a GETKEY command.
Then you can use an IF command to see if the key pressed equals the CHR$ code
for the function key and use a THEN clause to perform the desired operation(s).
The following example redefines function keys 2 and 3 to change screen colors,
switch to graphic mode 1, and draw a painted shape.
Note that redefinitions written in a program are still in effect when the program
ends. To restore the original definitions, press the reset button.
10 REM DEFINE KEYS 2 AND 3 AS CHR$ CODES 134 AND 135
20 KEY2,CHR$( 134): KEY3,CHR$( 135)
30 PRINT "PRESS P2 TO DRAW THE MOON. PRESS P3 TO DRAW
THE Sim."