Binary Search: Program Code ( visual basic )

Computer Science(9608) notes and Resources

I have written code for binary search in three different ways. 

1. Normal method but, here i have passed array value in parameter. This concept might be important for 9608.

Module Module1

    Sub Main()

        Dim item(5) As Integer

        Dim counter, temp, searchitem As Integer

        Console.WriteLine(" Enter 5 items: ")

        For counter = 1 To 5

            item(counter) = Console.ReadLine

        Next

        Console.Write(" Enter item to be searched: ")

        searchitem = Console.ReadLine()

        temp = BinarySearch(item, 1, 5, searchitem)

        If temp = -1 Then

            Console.WriteLine(" Item not found")

        Else

            Console.WriteLine(searchitem & " found at position " & temp)

        End If

        Console.ReadLine()

    End Sub

    Function BinarySearch(ByRef List() As Integer, ByVal Low As Integer, ByVal High As Integer, ByVal SearchItem As Integer) As Integer

        Dim Index, Middle As Integer

        Index = -1

        Do While (Index = -1) And (Low <= High)

            Middle = (High + Low) \ 2

            If List(Middle) = SearchItem Then

                Index = Middle

            ElseIf List(Middle) < SearchItem Then

                Low = Middle + 1

            Else

                High = Middle - 1

            End If

        Loop

        BinarySearch = Index

    End Function

End Module

2. Normal method 

Module Module1

    Sub Main()

        Dim list(5), middle As Integer

        Dim index, high, low, searchitem As Integer

        Console.WriteLine(" Enter 5 items: ")

        For index = 1 To 5

            list(index) = Console.ReadLine

        Next

        Console.Write(" Enter an item to be searched: ")

        searchitem = Console.ReadLine()

        low = 1

        high = 10

        Index = -1

        Do While (low <= high)

            middle = (high + low) \ 2

            If list(middle) = searchitem Then

                index = middle

                Console.WriteLine(" item found at position " & middle)

                Exit Do

            ElseIf list(middle) < searchitem Then

                low = middle + 1

            Else

                high = middle - 1

            End If

        Loop

        If (low > high) Then

            Console.WriteLine("not found")

        End If

        Console.ReadLine()

    End Sub

End Module

3. Recursive method

Module Module1

    Dim found As Integer

    Dim searchdata(5) As Integer

    Dim searchitem As Integer

    Sub Main()

        Dim low, high As Integer

        Dim counter As Integer

        Console.WriteLine(" Enter 5 items: ")

        For counter = 1 To 5

            searchdata(counter) = Console.ReadLine()

        Next

        Console.WriteLine("search value: ")

        searchitem = Console.ReadLine()

        low = 1

        high = searchdata.Length() - 1

        BinarySearch(low, high)

        If found = 0 Then

            Console.WriteLine(" Item not found")

        Else

            Console.WriteLine(" Item found at position " & found)

        End If

        Console.ReadLine()

    End Sub

    Function BinarySearch(low, high)

        Dim middle As Integer

        If low > high Then 

            Return 1

        End If 

        middle = ((high + low) / 2)

        If searchdata(middle) = searchitem Then

            found = middle

        ElseIf searchdata(middle) < searchitem Then

            BinarySearch(middle + 1, high)

        ElseIf searchdata(middle) > searchitem Then

            BinarySearch(low, middle - 1)

        End If

        Return 1

    End Function

End Module

                                                           - CIE A-LEVEL COMPUTER SCIENCE (  9608 )