WHILE...WEND Statement

 Action

 Executes a series of statements in a loop, as long as a given condition is
 true.

 Syntax


  WHILE  condition
  .

  .

  .


  WEND


 Remarks

 The argument  condition is  a numeric expression that BASIC evaluates as
 true (nonzero) or

  false (zero).

 If  condition is true (that is, if it does not equal zero), then any
 intervening statements are executed until the  WEND statement is
 encountered. BASIC then returns to the  WHILE statement and checks
 condition. If it is still true, the process is repeated. If it is not true
 (or if it equals zero), execution resumes with the statement following the
 WEND statement.

 Note

 BASIC's  DO... LOOP statement provides a more powerful and flexible
 loop-control structure.

  WHILE... WEND loops can be nested to any level. Each  WEND matches the most
 recent  WHILE. When BASIC encounters an unmatched  WHILE statement, it
 generates the error message WHILE without WEND. If BASIC encounters an
 unmatched  WEND statement, it generates the error message WEND without
 WHILE.

 Note

 Do not branch into the body of a  WHILE... WEND loop without executing the
 WHILE statement. This may cause run-time errors or program problems that are
 difficult to locate.

 See Also

  DO... LOOP

 Example


 The following example performs a bubble sort on the array A$. Assigning the
 variable Exchange a non-zero value (true) forces one pass through the
 WHILE... WEND loop (this construction is unnecessary with  DO... LOOP). When
 there are no more swaps, all elements of A$ are sorted, Exchange is false
 (equal to zero), and the program continues execution with the line following
 the  WEND statement.

 ' Bubble sort of array A$.

 CONST FALSE = 0, TRUE = -1

 DIM I AS INTEGER

 DIM A$(4)

 A$(1) = "New York"

 A$(2) = "Boston"

 A$(3) = "Chicago"

 A$(4) = "Seattle"

 Max = UBOUND(A$)

 Exchange = TRUE         ' Force first pass through the array.

 WHILE Exchange          ' Sort until no elements are exchanged.

    Exchange = FALSE

    ' Compare the array elements by pairs. When two are exchanged,

    ' force another pass by setting Exchange to TRUE.

    FOR I = 2 TO Max

       IF A$(I - 1) > A$(I) THEN

          Exchange = TRUE

          SWAP A$(I - 1), A$(I)

       END IF

    NEXT

 WEND

 CLS

 FOR I = 1 TO 4

    PRINT A$(I)

 NEXT I

 END