'Visual Basic 2010 Recursie Procedures en Functies
Module Exercise4Solution
    Sub Main()
        Dim numbers As Integer() = {1, 3, 4, 7, 9, 10, 11, 15, 18, 20}
        '
        Dim number, lowerbound, upperbound As Integer
        Dim found As Boolean
        '
        number = 15
        lowerbound = 0
        upperbound = 9
        found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found) ' True
        '
        number = 18
        lowerbound = 0
        upperbound = 7
        found = BinarySearch(number, numbers, lowerbound, upperbound)
        Console.WriteLine(found) ' False
        '
        Console.ReadLine()
    End Sub
    Function BinarySearch(ByVal number As Integer, _
                          ByVal array As Integer(), _
                          ByVal lowerbound As Integer, _
                          ByVal upperbound As Integer) As Boolean
        Dim middle As Integer = (lowerbound + upperbound) \ 2
        If (number = array(middle)) Then
            BinarySearch = True
        Else
            If (upperbound <= lowerbound) Then
                BinarySearch = False
            Else
                If number > array(middle) Then
                    lowerbound = middle + 1
                Else
                    upperbound = middle - 1
                End If
                BinarySearch = BinarySearch(number, array, lowerbound, upperbound)
            End If
        End If
    End Function
End Module
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