Arrays

An array holds a fixed number of values of the same type, accessed by a zero-based index in parentheses:

Module Program
    Sub Main()
        Dim scores() As Integer = {70, 85, 92}
        Console.WriteLine(scores(0))
        Console.WriteLine(scores.Length)

        scores(1) = 88
        Console.WriteLine(String.Join(", ", scores))

        Dim names(2) As String      ' upper bound 2: three elements
        names(0) = "Ada"
        names(1) = "Grace"
        names(2) = "Linus"
        Console.WriteLine(names.Length & " " & UBound(names))
    End Sub
End Module

70
3
70, 88, 92
3 2

Watch out: Dim names(2) As String gives the upper bound (the last index), not the length — so it creates three elements, 0 to 2. This is different from C#, where new string[2] has two.

Looping and common operations

Module Program
    Sub Main()
        Dim numbers = {5, 3, 8, 1, 9}

        For i = 0 To numbers.Length - 1
            Console.Write($"{i}:{numbers(i)} ")
        Next
        Console.WriteLine()

        Array.Sort(numbers)
        Console.WriteLine(String.Join(" ", numbers))
        Array.Reverse(numbers)
        Console.WriteLine(String.Join(" ", numbers))
        Console.WriteLine(Array.IndexOf(numbers, 8))
        Console.WriteLine(numbers.Contains(4))
        Console.WriteLine($"{numbers.Sum()} {numbers.Max()} {numbers.Average()}")
    End Sub
End Module

0:5 1:3 2:8 3:1 4:9
1 3 5 8 9
9 8 5 3 1
1
False
26 9 5.2

Sum, Max, Average, and Contains come from LINQ, which VB imports automatically — Level 2 covers it in depth.

Resizing with ReDim

Module Program
    Sub Main()
        Dim items() As String = {"a", "b"}
        ReDim Preserve items(3)
        items(2) = "c"
        items(3) = "d"
        Console.WriteLine(String.Join(",", items))

        ReDim items(1)
        Console.WriteLine(items(0) Is Nothing)
    End Sub
End Module

a,b,c,d
True

ReDim Preserve resizes and keeps the contents; plain ReDim starts over. Resizing copies the whole array, so when a collection grows often, use a List(Of T) instead (Level 2).

Multidimensional arrays

Module Program
    Sub Main()
        Dim grid(2, 3) As Integer      ' 3 rows, 4 columns
        For r = 0 To 2
            For c = 0 To 3
                grid(r, c) = r * 10 + c
            Next
        Next
        Console.WriteLine(grid(2, 3))
        Console.WriteLine(grid.GetLength(0) & " x " & grid.GetLength(1))

        Dim board(,) As Char = {{"X"c, "O"c}, {"O"c, "X"c}}
        Console.WriteLine(board(1, 0))
    End Sub
End Module

23
3 x 4
O

Practice

Store seven daily temperatures in an array, then print the average (one decimal), the highest value, and how many days were above 20.

Module Program
    Sub Main()
        Dim temps = {18, 21, 25, 19, 23, 17, 22}
        Dim warmDays = 0
        For Each t In temps
            If t > 20 Then warmDays += 1
        Next
        Console.WriteLine($"Average: {temps.Average():F1}")
        Console.WriteLine($"Highest: {temps.Max()}")
        Console.WriteLine($"Days above 20: {warmDays}")
    End Sub
End Module

Average: 20.7
Highest: 25
Days above 20: 4