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Q40553: Bad Results with Recursion of STATIC Procedure in QB.EXE

Article: Q40553
Product(s): See article
Version(s): 4.00 4.00B 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist4.00 buglist4.00b buglist4.50 SR# S890113-13 | mspl13_basic
Last Modified: 23-JAN-1989

The use of the STATIC clause in recursive functions or SUBprograms
should be avoided. Using STATIC may cause you to overwrite values from
a previous CALL. For example, recursively CALLing a STATIC SUBroutine
and decrementing the passed parameter actually will change the value
of the parameter when the procedure returns at the END SUB statement.
However, the QuickBASIC editor incorrectly allows the recursive use of
a STATIC subroutine or function without any side effects of changing
the passed parameters. This problem can lead to subtle programming
errors because the incorrect results don't become apparent until
compile time.

More information on recursion in Version 4.00 or 4.00b can be found
on Pages 81-82 of "Microsoft QuickBASIC 4.0: Programming in BASIC:
Selected Topics." For QuickBASIC Version 4.50, recursion is documented
on Pages 71-72 of "Microsoft QuickBASIC: Programming in BASIC."

The following is a code example:

DECLARE SUB anysub (Param#)
CLS
 Param# = 10#
 CALL anysub(Param#)
END

SUB anysub (Param#) STATIC
  IF Param# > 1 THEN
     CALL anysub(Param# - 1)
  END IF
  PRINT Param#;
END SUB

You will get the following results when this code sample is run in the
QB.EXE editor:

1  2  3  4  5  5  6  7  8  9  10

You will get the following results when it is run as an executable
.EXE program:

1  1  1  1  1  1  1  1  1  1  10

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