Length, array. How many elements are in an array? In VB.NET programs, we must account for empty arrays, 1D arrays, and sometimes 2D arrays.

With properties like Length and LongLength, we get values that indicate array element count. These values are stored by the arrays, so they are fast to access.

Example. We use the Main Subroutine to run some array-length testing code. We first need to create some arrays—we initialize a 3-element String array.

Module Module1
    Sub Main()

        ' Part 1: access Length property.
        Dim array1() as String = { "cat", "apple", "frog" }
        Dim length1 as Integer = array1.Length
        Console.WriteLine("LENGTH: {0}", length1)

        ' Part 2: access LongLength.
        Dim longLength1 as Long = array1.LongLength
        Console.WriteLine("LONGLENGTH: {0}", longLength1)

        ' Part 3: get Length of zero-length array.
        Dim array2() as Integer = { }
        Dim length2 = array2.Length
        Console.WriteLine("LENGTH: {0}", length2)

        ' Part 4: get length for rank 0 of first array.
        Dim length3 = array1.GetLength(0)
        Console.WriteLine("LENGTH: {0}", length3)

    End Sub
End Module
LENGTH: 3
LONGLENGTH: 3
LENGTH: 0
LENGTH: 3

2D arrays. Consider now 2D arrays—these have a total length of elements, but each dimension (or rank) also has a length. The GetLength() function returns the length for a certain rank.

Module Module1
    Sub Main()

        ' Use GetLength on 2D array.
        Dim two(,) As Integer = New Integer(,) { { 10, 20 }, { 30, 40 }, { 50, 60 } }
        Console.WriteLine("GETLENGTH: {0}", two.GetLength(0))
        Console.WriteLine("GETLENGTH: {0}", two.GetLength(1))

        ' Use Length on 2D array.
        Console.WriteLine("LENGTH: {0}", two.Length)
        
    End Sub
End Module
GETLENGTH: 3
GETLENGTH: 2
LENGTH: 6

Summary. In VB.NET, all arrays know their lengths, and this value can be accessed instantly with Length. For 2D arrays, the situation is more complex, but GetLength can be used.