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Q46847: INKEY$ Example to Work Around ON KEY GOSUB Suspended by INPUT

Article: Q46847
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 | SR# S890703-77 B_GWBasicI B_BasicCom | mspl13_basic
Last Modified: 19-OCT-1990

This article includes a sample program demonstrating how to emulate a
cursor during an INKEY$ loop, and how to trap the ESC, ENTER, and
BACKSPACE keys using the INKEY$ function. This program allows you to
enter text into a variable while supporting the option to exit the
data entry by pressing the ESC key or the ENTER key. The BACKSPACE key
lets you delete input data in this INKEY$ example.

You may be motivated to use the INKEY$ function to accept user input
because ON KEY GOSUB event trapping is suspended during an INPUT or
LINE INPUT statement or an INPUT$ function. Instead of using ON KEY
GOSUB event trapping to detect special key presses during input, and
instead of using INPUT, LINE INPUT, or INPUT$ for your input, you can
use the INKEY$ function in a continuous loop to process all keys.

This information applies to the following:

1. Microsoft GW-BASIC Interpreter versions 3.20, 3.22, and 3.23 for
   MS-DOS

2. Microsoft QuickBASIC versions 1.00, 1.01, 1.02, 2.00, 2.01, 3.00,
   4.00, 4.00b, and 4.50 for MS-DOS

3. Microsoft BASIC Compiler versions 6.00, and 6.00b for MS-DOS
   and MS OS/2

4. Microsoft BASIC PDS versions 7.00 and 7.10 for MS-DOS and MS OS/2

The trapping of keys using the ON KEY GOSUB statement is temporarily
suspended while INPUT, INPUT$, or LINE INPUT is pending. If a key
being trapped by ON KEY GOSUB is pressed while an INPUT, INPUT$, or
LINE INPUT is pending, the first occurrence of that event is remembered
but is not executed until you satisfy the INPUT, INPUT$, or LINE
INPUT. Only one key press for a given ON KEY GOSUB trap is remembered
while an INPUT, INPUT$, or LINE INPUT is pending.

As an alternative to using ON KEY GOSUB, and in order to continue
event trapping during input, you can write a routine to input and
process one character at a time using the INKEY$ function in a loop.
Such a program example is shown at the bottom of this article.

Related Topics
--------------

Note: INKEY$ returns a 2-byte STRING for all keys returning an
extended keyboard KEY code, such as function keys F1 through F10. For
additional information on this topic, query in this Knowledge Base
using the following words:

   INKEY$ and EXTENDED and 2-byte codes

If you want to use both INKEY$ and ON KEY GOSUB trapping in the same
program, you must take into account an extra required key press, as
explained in a separate article, which may be found by querying using
the following words:

   INKEY$ and trap and additional and key and press

For more information about the ON KEY GOSUB statement's key trapping
being suspended by INPUT$, INPUT, or LINE INPUT, search for a separate
article using the following words:

   LINE INPUT and event and suspended

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

When invoking INKEY$ in a loop, no cursor automatically displays
(unlike for the INPUT or LINE INPUT statement). The following code
example demonstrates how to emulate a cursor during an INKEY$ loop and
also trap the ESC, the ENTER, and the BACKSPACE keys.

'          INPTCHAR.BAS
'    Written under QuickBASIC 4.50
' Note: Line Labels, DECLARE, SELECT CASE, and SUBprograms are not
' supported under GW-BASIC. The program would need to be
' rewritten for GW-BASIC; however, the same principles using
' INKEY$ apply to GW-BASIC.
DECLARE SUB Cursor ()
DECLARE SUB GetKey (a$)
Col = 1
Row = 7
NewCol = 1
CLS
PRINT "---------------------------------------------------------"
PRINT "This program will allow you to enter text into a"
PRINT "variable while having control to exit the data entry with"
PRINT "the ESCape key or the ENTER key. The BACKSPACE key is"
PRINT "functional for editing."
PRINT "---------------------------------------------------------"
LOCATE Row, NewCol
Cursor                   ' Emulate DOS cursor on screen

DO WHILE NewCol < 81
   LOCATE Row, NewCol
   GetKey a$             ' Get User input
   SELECT CASE ASC(a$)   ' Evaluate the character input from the
                         ' keyboard
      CASE 13, 27        ' Codes for CARRIAGE RETURN and ESCAPE
         GOTO Done
      CASE 8             ' Code for BACKSPACE
         GOSUB Backspace
      CASE ELSE
         WholeLine$ = WholeLine$ + a$
         LOCATE Row, Col
         PRINT WholeLine$;
         Cursor
         NewCol = LEN(WholeLine$) + 1
   END SELECT
LOOP

Done:               ' The ESCape key or ENTER key was pressed
   LOCATE Row, Col
   PRINT WholeLine$ + " "
   PRINT
   PRINT "The String you Entered is:  "; WholeLine$
   END

Backspace:          ' The BACKSPACE key was pressed
   LOCATE Row, LEN(WholeLine$): PRINT "  "
   WholeLine$ = LEFT$(WholeLine$, LEN(WholeLine$) - 1)
   LOCATE Row, Col
   PRINT WholeLine$;
   Cursor
   RETURN

SUB Cursor
   COLOR 23
   PRINT "▄"
   COLOR 7
END SUB

SUB GetKey (a$)
   DO
      a$ = INKEY$
   LOOP WHILE a$ = ""
END SUB

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