Q45909: Example of How to Use 1- and 2-Byte Return Codes from INKEY$

Article: Q45909
Product(s): See article
Version(s): 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890606-37 B_BasicCom | mspl13_basic
Last Modified: 13-DEC-1989

The following information applies to QuickBASIC Versions 3.00, 4.00,
4.00b, and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b,
and to Microsoft PDS Version 7.00. The Version 4.50 QuickBASIC Advisor
and the BASIC PDS 7.00 Microsoft Advisor on-line Help system state the
following:

   The INKEY$ function returns a 1- or 2-byte string containing a
   character read from the standard input device. A null string is
   returned if no character is waiting there. A 1-character string
   contains the actual character read from the keyboard, while a
   2-character string indicates an extended code, the first character
   of which is hexadecimal 00.

When two bytes are received from an extended key, the second character
of the string is the scan code associated with the extended key. The
chart in the Version 4.50 QuickBASIC Advisor and Microsoft Advisor
on-line Help system for BASIC PDS 7.00 contains the scan code listing.
The extended keys include the function keys, arrow keys, HOME, PGUP,
END, PGDN, and SHIFT+TAB keys.

The following program example demonstrates how to use the INKEY$
function to return either a 1-byte character or 2-byte extended code.
The length, ASCII representation, and the numeric representation for
each key that is pressed are displayed. In addition, the arrow keys
and the SHIFT+TAB key combination are trapped for 2-byte returns, and
the ESC, TAB, and SPACEBAR are trapped for 1-byte returns.

Code Example
------------

'SCAN CODES to be used with a 2-byte return code from INKEY$
CONST left = &H4B
CONST right = &H4D
CONST up = &H48
CONST down = &H50
CONST tabscan = 15

'ASCII CODES  to be used with a 1-byte return from INKEY$
CONST escape = 27
CONST tabchar = 9
CONST space = 32

DO UNTIL UCASE$(t$) = "Q"  'PROGRAM ENDS WHEN 'Q' OR 'q' IS ENTERED
 CLS
 LOCATE 23, 35
 PRINT "Q to quit"
 t$ = INKEY$
 IF t$<>"" THEN
  LOCATE 10, 1
  length% = LEN(t$)
  PRINT "length "; length%
  PRINT "ASCII representation "; t$
  PRINT "numeric representation ";
  SELECT CASE length%
         CASE 2
           FOR i = 1 TO 2
             PRINT ASC(MID$(t$, i, 1)); " ";
           NEXT i
                 SELECT CASE ASC(RIGHT$(t$, 1))
                         CASE up
                          PRINT "up           "
                         CASE down
                          PRINT "down         "
                         CASE left
                          PRINT "left         "
                         CASE right
                          PRINT "right        "
                         CASE tabscan
                          PRINT "Shift tab"
                 END SELECT
         CASE 1
           PRINT ASC(t$);
           SELECT CASE ASC(LEFT$(t$, 1))
                 CASE escape
                   PRINT "escape       "
                 CASE tabchar
                   PRINT "tab character"
                 CASE space
                   PRINT "space        "
           END SELECT
         CASE ELSE
           PRINT "                    "
  END SELECT
 END IF
LOOP
END