Q42474: "Array Not Defined"; Must DIMension Array Above Its First Use

Article: Q42474
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890313-67 B_BasicCom | mspl13_basic
Last Modified: 18-DEC-1989

Microsoft QuickBASIC Versions 4.00 4.00b and 4.50, Microsoft BASIC
Compiler Versions 6.00 and 6.00b, and Microsoft BASIC PDS Version 7.00
are single-pass compilers. This means that all arrays (static or
dynamic) that are to be used within a BASIC program must be
DIMensioned physically above where they are first used. The exception
to this is when they are dynamically declared in a COMMON statement.

The program below demonstrates how the array dimension is unknown when
an attempt is made to pass the array to a SUBprogram, even though it
is DIMensioned logically before it is used. The resulting error will
be "Array not defined" on the CALL statement. This is expected
behavior in QuickBASIC, Microsoft BASIC Compiler, and BASIC PDS. The
program is as follows:

DECLARE SUB GetStartPos (letterWidth!())
DEFINT A-Z
GOSUB DimLetterWidths
CALL GetStartPos(letterWidth!())
END

DimLetterWidths:
  REDIM SHARED letterWidth! (128)  ' REDIM dimensions a dynamic array.
  RETURN

SUB GetStartPos (letterWidth!())
  PRINT UBOUND (letterWidth!, 1)
END SUB

If the array is declared as dynamic by a COMMON statement, the error
does not occur. Placing the statement COMMON letterWidth!() after the
DEFINT A-Z line eliminates the error.

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