Q61440: DIMension in a FOR-NEXT Loop Is Possible

Article: Q61440
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900412-54 B_BasicCom | mspl13_basic
Last Modified: 10-MAY-1990

Microsoft QuickBASIC allows you to correctly DIMension a static array
within a loop (FOR, WHILE, or DO). This is possible because a DIM of a
static array happens as the program is being compiled (or during the
binding phase in the interpreter). DIM on a static array is not an
executable statement. Even though the DIM appears in a loop, it is not
being executed over and over as the loop iterates. Each time the loop
executes, the array is not being redimensioned. Therefore, any values
inserted into the array are not lost.

This information applies to Microsoft QuickBASIC versions 4.00, 4.00b,
and 4.50, to Microsoft BASIC Compiler versions 6.00 and 6.00b, and to
Microsoft BASIC Professional Development System (PDS) version 7.00.

The situation is different for dynamic arrays. QuickBASIC will give
you an error on a DIMension of a dynamic array in a loop. If an array
needs to be redimensioned as a loop executes, the program should REDIM
the array in the loop. REDIM is an executable statement, and
therefore, will be executed over and over as the loop repeats. As the
loop executes, REDIM will reallocate the memory for that array and
erase its previous contents.

The following code example demonstrates this feature of BASIC:

c% = 100
FOR i% = 1 TO 20
'  DIM a%(c%)   ' will generate an error.
'  REDIM a%(c%) ' will redim the array and erase its contents.
   DIM a%(20)
   a%(i%)=i%
   PRINT a%(i%)
NEXT i%

FOR j% = 1 TO 20
   PRINT a%(j%)
NEXT j%

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