binary search with a homemade algorithm

Question

task I need a binary search with a homemade algorithm.

Now the program should work, but unfortunately this is not the case, he compares it but problem is he charging cities. than those in the output if not found is displayed.

The purpose of this exercise is that the search values ​​are compared with the zipcodes. zipcodes contain so a postal code and the name of the city.

Module Module1

    Sub Main()
        '                           0       1          2       3            4       5         6       7         8       9     
        Dim zipcodes() As String = {"1000", "Brussel", "2000", "Antwerpen", "3000", "Leuven", "8000", "Brugge", "9000", "Gent"}
        'Dim zipcodesCount As Integer = 5
        '
        Dim searchValues() As String = {"0500", "1000", "2000", "3000", "4000", "8000", "9000", "9500"}
        ' 
        Dim searchValueIndex As Integer
        For searchValueIndex = 0 To 7
            Dim searchValue As String = searchValues(searchValueIndex)
            '
            Dim index As Integer
            Dim found As Boolean = False
            Dim allesDoorzocht As Boolean = False

            Dim uBound, lBound As Integer
            uBound = zipcodes.GetUpperBound(0) - 1
            lBound = zipcodes.GetLowerBound(0)


            Do Until found OrElse allesDoorzocht

                index = (lBound + uBound + 1 ) \ 2

                If (searchValue = zipcodes(index)) Then
                    found = True
                End If

                If uBound <= lBound Then
                    allesDoorzocht = True
                End If

                If Not (found OrElse allesDoorzocht) Then

                    If searchValue > zipcodes(index) Then
                        lBound = index + 1
                    Else
                        uBound = index - 1
                    End If

                End If

            Loop


            If found Then
                Console.WriteLine(searchValue & " is zipcode of " & zipcodes(index + 1))
                ' Of : Console.WriteLine(searchValue & " is zipcode of " & zipcodes(index + 1))
            Else
                Console.WriteLine(searchValue & " not found")
            End If
        Next
        '
        Console.ReadLine()
    End Sub
End Module

Answer 1

Create City objects

Public Class City
    Public Property ZipCode As String 
    Public Property Name As String 
End Class

and work with arrays of City instead

Dim citiy() As City = { _
    New City With { .ZipCode = "1000", .Name = "Brussel" }, _
    New City With { .ZipCode = "2000", .Name = "Antwerpen" }, _
    New City With { .ZipCode = "3000", .Name = "Leuven" }, _
    New City With { .ZipCode = "8000", .Name = "Brugge" }, _
    New City With { .ZipCode = "9000", .Name = "Gent" } _
}

Now you can access zip codes and names like this

city(i).ZipCode
city(i).Name

and corresponding city names and zip codes have the same index.

---

Note I am using automatic properties and object initializers that have been introduced with VS 2010. You can probably drop the line continuation signs _. (I am still working with VS 2008 and usually C#)

Answer 2

You are searching the array zipcodes which should be in ascending order for the binary search you wrote, but "1000"<="Brussel"<="2000" is not true. You have to make sure that your algorithm only regards the even elements of your array. You did that perfectly by splitting. But in the not found case, you have to make sure that bounds are still pointing to even indices and not the city names. So you have to do lBound=index+2 or uBound=index-2.