Q35969: Do Not Mix Arrayname AS Type and % Type Suffix in DIM/COMMON

Article: Q35969
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom buglist4.00 buglist4.00b buglist4.50 | mspl13_basic
Last Modified: 13-DEC-1989

Do not mix the use of "AS Type" declaration syntax with explicit type
declaration suffixes (%, &, !, #, and $) with a given array name that
occurs in both DIM and COMMON statements. Programs should be run in
the QuickBASIC QB.EXE editor to catch such a mismatch error.

If you compile Example Program 1 (below) with the BC /D (debug)
option, then the .EXE file will produce an error at run time. If you
do not compile with BC /D (debug) option, then the mismatched
DIM/COMMON declaration will not be detected, and the resulting .EXE
file will hang the machine, requiring a cold boot.

This article applies to Microsoft QuickBASIC 4.00, 4.00b, and 4.50 and
to Microsoft BASIC Compiler Versions 6.00 and 6.00b (buglist6.00,
buglist6.00b) for MS-DOS and MS OS/2. This problem was corrected in
Microsoft BASIC PDS Version 7.00 (fixlist7.00) for MS-DOS and MS OS/2.

----------------

For the example program below, BASIC PDS 7.00 produces the following
message for this error:

COMMON SHARED /x/ x() AS INTEGER   ' AS INTEGER used for type declare.
                         ^ AS clause required on first declaration

In Example Program 1, the array x% is treated as different from array
x.  Because the AS clause takes precedence over the "%" type suffix,
BC.EXE declares the array x in COMMON as a dynamic array, replacing
the static array x% that was dimensioned with the DIM statement. Thus,
when the final .EXE is run, array bounds are exceeded, and the machine
hangs (without BC /D) or gives a run-time error (with BC /D).

When run in the QB.EXE editor, the following program gives the error
"AS Clause required in first declaration" due to illegal mixing of
type declaration methods:

' Example Program 1
DIM x%(100)    ' % used for type declaration
COMMON SHARED /x/ x() AS INTEGER   ' AS INTEGER used for type declare.
FOR i% = 0 TO 99
  PRINT "i% = "; i%
  x%(i%) = 1
NEXT i%

The following program shows a correct method for type declaration:

' Example Program 2
DIM x%(100)
COMMON SHARED /x/ x%()
FOR i% = 0 TO 99
  PRINT "i% = "; i%
  x%(i%) = 1
NEXT i%

The following program shows another correct method for type declaration:

' Example Program 3
DIM x(100) AS INTEGER
COMMON SHARED /x/ x() AS INTEGER
FOR i% = 0 TO 99
  PRINT "i% = "; i%
  x(i%) = 1
NEXT i%

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