Q31170: SELECT, IF, FOR, DO, WHILE, CASE, and SUB Structure Errors

Article: Q31170
Product(s): See article
Version(s): 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | | mspl13_basic
Last Modified: 21-DEC-1989

A common programming error is to incorrectly close one type of
control structure inside another. In many cases, you may get an error
message that does not seem to apply. However, if you look more
closely, you will find a structure in the program that was not
properly closed.
   The following are errors that you can receive in QuickBASIC when
you have improperly nested control structures:

   1. CASE               without SELECT
   2. ELSE               without IF
   3. IF                 without END IF
   4. END IF             without block IF
   5. FOR                without NEXT
   6. NEXT               without FOR
   7. DO                 without LOOP
   8. LOOP               without DO
   9. WHILE              without WEND
  10. WEND               without WHILE
  11. SELECT             without END SELECT
  12. SUB/FUNCTION       without END SUB/FUNCTION
  13. END SUB/FUNCTION   without SUB/FUNCTION

   If one of the above errors occurs, one of the following situations
has occurred:

   1. A control structure has been opened but never closed.
   2. A control structure has been closed but never opened.
   3. A control structure has been closed outside of the block it
controls.

   The following program demonstrates the problem:

REM This program executes correctly and does not
REM produce any error messages. However, the nature of
REM the code is complex enough that it can easily lead to
REM an improper error message if the control structures
REM are not terminated properly. For example, deleting any
REM line of this program causes a control structure error.

SUB MySub
 SELECT CASE x
    CASE 1
       IF 0 THEN
         FOR i = 1 TO x
            DO
               WHILE 0
               WEND
            LOOP UNTIL 0
         NEXT i
       ELSE IF 0 THEN x = 1
       END IF
    CASE ELSE
 END SELECT
END SUB

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.