Q61346: Dynamic Array Using INT in FOR Loop Returns Bad Results

Article: Q61346
Product(s): See article
Version(s): 7.00   | 7.00
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | SR# S900409-113 buglist7.00 fixlist7.10 | mspl13_basic
Last Modified: 20-SEP-1990

Assigning values to a dynamic array using the INT function in a FOR
loop that contains a variable for the maximum index can produce
incorrect results when compiled. The problem seems to be an addressing
problem where all array values contain the result of the last
computation.

Microsoft has confirmed this to be a problem in the BC.EXE environment
of Microsoft BASIC Professional Development System (PDS) version 7.00.
This problem was corrected in BASIC PDS 7.10. This problem does not
occur in the QBX.EXE editor in 7.00, or in earlier versions of
Microsoft QuickBASIC or Microsoft BASIC Compiler.

Any of the following workarounds will correct this problem:

1. Compile with the BC /D compiler option.
2. Use a static array.
3. Use a temporary variable for the function value.
4. Use a literal to define the FOR loop.

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

The following code example demonstrates the problem:

   'Compile and link lines:
   '
   ' BC FORARRAY;               NOTE: The BC /D compiler option
   '                                  corrects the problem.
   ' LINK FORARRAY;
   DEFINT A-Z                   'Any numeric type shows problem.
   n = 1                        'n=1 is required for FOR upper index.
   DIM a(n)                   'Array must be dynamic to show problem.
   a(0) = 1
   a(1) = 2
   FOR i = 0 TO n               'Variable n required to cause problem.
      a(i) = INT(a(i))          'INT or FIX functions cause problem.
      PRINT a(i)       'Incorrectly prints 2 for each iteration; it
                       'should have printed 1, then 2.
   NEXT
   END

When compiled without /D, the above program displays the following
incorrect results:

   2
   2

When run in the QBX.EXE editor or compiled with /D option, the above
program displays the following correct results:

   1
   2

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