' version 11-03-2016
' compile with: fbc -s console

#Include Once "crt/stdlib.bi"      ' needed for qsort subroutine

' Declare Sub qsort (ByVal As Any Ptr, <== point to start of array
'                    ByVal As size_t,  <== size of array
'                    ByVal As size_t,  <== size of array element
' ByVal As Function(ByVal As Any Ptr, ByVal As Any Ptr) As Long)  <== callback function
' declare callback function with Cdecl to ensures that the parameters are passed in the correct order
'
' size of long: 4 bytes on 32bit OS, 8 bytes on 64bit OS

' ascending
 Function callback Cdecl (ByVal element1 As Any Ptr, ByVal element2 As Any Ptr) As Long
     Function = *Cast(Long Ptr, element1) - *Cast(Long Ptr, element2)
End Function

' Function callback Cdecl (ByVal element1 As Any Ptr, ByVal element2 As Any Ptr) As Long
' Dim As Long e1 = *Cast(Long Ptr, element1)
' Dim As Long e2 = *Cast(Long Ptr, element2)
' Dim As Long result = Sgn(e1 - e2)
' If Sgn(e1) = -1 And Sgn(e2) = -1 Then result = -result
'     Function = result
' End Function

' ------=< MAIN >=------

Dim As Long i, array(20)

Dim As Long lb = LBound(array)
Dim As Long ub = UBound(array)

For i = lb To ub     ' fill array
    array(i) = 10 - i
Next

Print
Print "unsorted array"
For i = lb To ub     ' display array
    Print Using "###";array(i);
Next
Print : Print

' sort array
qsort(@array(lb), ub - lb +1, SizeOf(array), @callback)

Print "sorted array"
For i = lb To ub     ' show sorted array
    Print Using "###";array(i);
Next
Print

' empty keyboard buffer
While Inkey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End