SELECT, IF, FOR, DO, WHILE, CASE, and SUB Structure Errors (31170)

SUMMARY

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

MORE INFORMATION

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

A control structure has been opened but never closed.
A control structure has been closed but never opened.
A control structure has been closed outside of the block itcontrols.

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