Q30844: INKEY$ Returns Two-Byte String for Arrow and Function Keys

Article: Q30844
Product(s): See article
Version(s): 1.00 1.01 1.02 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 21-APR-1989

The INKEY$ function returns a one- or two-byte string. Alphanumeric
keys return one-byte strings. The function keys and the directional
keys return two-byte strings.

If INKEY$ returns a two-byte string, then each byte needs to be
examined to determine the key that was pressed. For two-byte strings,
the first byte will always be null [an ASCII value of zero, CHR$(0)],
and the second byte will be the key's scan code. The LEN function
tells you the length of the returned string (one byte or two).

This information applies to Microsoft QuickBASIC Versions 1.00, 1.01,
2.00, 2.01, 3.00, 4.00, 4.00b, and 4.50 for MS-DOS, and to the
Microsoft BASIC Compiler Versions 6.00 and 6.00b for MS-DOS and OS/2.

The keyboard scan codes are listed in the BASIC language reference
manual in the KEY(n) statement section.

Example 1

The following sample code prints a message if the UP ARROW key is
pressed:

top:
I$ = INKEY$
'The scan code for the UP ARROW is &H48:
IF I$ = CHR$(0) + CHR$(&H48) THEN
   PRINT "up arrow key pressed"
END IF
GOTO top

Example 2

The following code example shows how to print the ASCII value of any
key pressed:

REM     ASCII.BAS
CLS
PRINT "Hit F1 To Exit"
PRINT:PRINT
DO
   A$=INKEY$
   IF MID$(A$,1,1) <> "" THEN
      PRINT A$
      PRINT "ASCII Value = "; ASC(A$)
   END IF
   IF MID$(A$,2,1) <> "" THEN
      PRINT "ASCII Value = "; ASC(MID$(A$,2,1))
   END IF
LOOP UNTIL MID$(A$,2,1) = CHR$(59)
END

Program note: The DO...LOOP statement is only supported in QuickBASIC
3.00 or later. In earlier versions, you can rewrite this example to
use a different loop, such as WHILE...WEND.

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