Pete's QBASIC Site

Code: Select all

Option Explicit On 

Module Main

  Public Sub Main()

  Dim ssource(5) As String

    ssource(0) = "alpha"
    ssource(1) = "beta"
    ssource(2) = "cow"
    ssource(3) = "monster"
    ssource(4) = "monsters go"
    ssource(5) = "zzzz"

    Debug.WriteLine(search(ssource, "monsters go"))

  End Sub

  Public Function search(ByVal ssource() As String, ByVal starget As String) As Long

  Dim lhigh As Long = UBound(ssource)
  Dim llow As Long = -1
  Dim lprobe As Long

    While (lhigh - llow > 1)

      lprobe = (lhigh + llow) \ 2
        If (ssource(lprobe) < starget) Then
           llow = lprobe
        Else
           lhigh = lprobe
        End If

    End While

    If (lhigh = UBound(ssource) Or ssource(lhigh) <> starget) Then
       Return -1
    Else
       Return lhigh
    End If

  End Function

  Public Function search(ByVal lsource() As Long, ByVal ltarget As Long) As Long

  Dim lhigh As Long = UBound(lsource)
  Dim llow As Long = -1
  Dim lprobe As Long

    While (lhigh - llow > 1)

      lprobe = (lhigh + llow) \ 2
        If (lsource(lprobe) < ltarget) Then
           llow = lprobe
        Else
           lhigh = lprobe
        End If

    End While

    If (lhigh = UBound(lsource) Or lsource(lhigh) <> ltarget) Then
       Return -1
    Else
       Return lhigh
    End If

  End Function

End Module