' FB 1.05.0 Win64

Sub quicksort(a() As Double, first As Integer, last As Integer)
  Dim As Integer length = last - first + 1
  If length < 2 Then Return
  Dim pivot As Double = a(first + length\ 2)
  Dim lft As Integer = first
  Dim rgt As Integer = last
  While lft <= rgt
    While a(lft) < pivot
      lft +=1
    Wend
    While a(rgt) > pivot
      rgt -= 1
    Wend
    If lft <= rgt Then
       Swap a(lft), a(rgt)
       lft += 1
       rgt -= 1
    End If
  Wend
  quicksort(a(), first, rgt)
  quicksort(a(), lft, last)
End Sub

Function median(a() As Double) As Double
  Dim lb As Integer = LBound(a)
  Dim ub As Integer = UBound(a)
  Dim length As Integer = ub - lb + 1
  If length = 0 Then Return 0.0/0.0 '' NaN
  If length = 1 Then Return a(ub)
  Dim mb As Integer = (lb + ub) \2
  If length Mod 2 = 1 Then Return a(mb)
  Return (a(mb) + a(mb + 1))/2.0
End Function

Dim a(0 To 9) As Double = {4.4, 2.3, -1.7, 7.5, 6.6, 0.0, 1.9, 8.2, 9.3, 4.5}
quicksort(a(), 0, 9)
Print "Median for all 10 elements  : "; median(a())
' now get rid of final element
Dim b(0 To 8) As Double = {4.4, 2.3, -1.7, 7.5, 6.6, 0.0, 1.9, 8.2, 9.3}
quicksort(b(), 0, 8)
Print "Median for first 9 elements : "; median(b())
Print
Print "Press any key to quit"
Sleep