The binary search algorithm

This lesson covers implementing binary search in VB.NET, with the aim of understanding how to find a value efficiently.

Binary search halves the search range each time over an already-sorted array. It reaches the target in far fewer steps than a linear search that checks each element in turn.

The sample code calculates the middle mid from the two positions low and high, compares it with the target, and narrows the range by updating low or high. The \ operator is integer division, discarding anything after the decimal point.

A common early stumble is that binary search requires the array to be sorted beforehand. Run it on an unsorted array and the answer may simply be wrong.

In professional work, the idea behind binary search is applied widely wherever a particular value has to be found quickly in a large body of data — dictionary lookups, database indexes.

📖 Reference code

Function BinarySearch(arr() As Integer, target As Integer) As Integer
    Dim low As Integer = 0
    Dim high As Integer = arr.Length - 1
    While low <= high
        Dim mid As Integer = (low + high) \ 2
        If arr(mid) = target Then
            Return mid
        ElseIf arr(mid) < target Then
            low = mid + 1
        Else
            high = mid - 1
        End If
    End While
    Return -1
End Function

Dim nums() As Integer = {1, 3, 5, 7, 9, 11}
Console.WriteLine(BinarySearch(nums, 7))
Console.WriteLine(BinarySearch(nums, 4))

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run VB.NET directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).