'==============================================================================
'
' Example code for sorting a virtual long integer array
' Copyright (c) 1997 by PowerBASIC, Inc. All Rights Reserved.
'
' This code can easily be adapted to other data types.
'
'==============================================================================

$STACK 4096

IF FRE(-11) = 0 THEN
  PRINT "EMS not available for virtual arrays"
  END
END IF

DIM i AS LONG
DIM u AS LONG

u = 5000

DIM VIRTUAL x(u) AS LONG

PRINT "Filling array..."
FOR i = 0 TO u
  x(i) = RND(0, u)
NEXT i

PRINT "Sorting array..."
SortVlong x()

FOR i = 0 TO u
  PRINT x(i)
NEXT i

'------------------------------------------------------------------------------
' Sort a string array using a quick-sort.  Works with both standard and
' virtual arrays.  Calls a recursive quicksort sub to do the actual work.
'
SUB SortVlong(vArray(1) AS LONG) PUBLIC

  DIM l AS LONG
  DIM u AS LONG

  l = LBOUND(vArray(1))
  u = UBOUND(vArray(1))

  QSort vArray(), l, u

END SUB

'------------------------------------------------------------------------------
' Recursive QuickSort
'
SUB QSort(vArray(1) AS LONG, lowbound AS LONG, hibound AS LONG) PRIVATE

  DIM low AS LONG
  DIM high AS LONG

  DIM midval AS LONG
  DIM temp AS LONG

  low = lowbound
  high = hibound
  midval = vArray((low + high) / 2)

  WHILE (low <= high)

    WHILE vArray(low) < midval AND low < hibound
      INCR low
    WEND

    WHILE midval < vArray(high) AND high > lowbound
      DECR high
    WEND

    IF (low <= high) THEN
      ' SWAP statement is not supported with virtual arrays
      temp = vArray(low)
      vArray(low) = vArray(High)
      vArray(high) = temp

      INCR low
      DECR high
    END IF

  WEND

  IF (lowbound < high) THEN
    QSort vArray(), lowbound, high
  END IF

  IF (low < hibound) THEN
    QSort vArray(), low, hibound
  END IF

END SUB