Question

In this part of the Visual Basic programming tutorial, we will cover arrays. We will initiate arrays and read data from them.

Arrays are collections of data. A variable can hold only one item at a time. Arrays can hold multiple items. These items are called elements of the array. Arrays store data of the same data type. Each element can be referred to by an index. Arrays are zero based. The index of the first element is zero.

Collections serve the similar purpose. They are are more powerful than arrays. They will be described later.

Arrays are used to store data of our applications. We declare arrays to be of a certain data type. We specify their length. And we initialize arrays with data. We have several methods for working with array. We can modify the elements, sort them, copy them or search them.

Initializing arrays

There are several ways, how we can initialize an array in Visual Basic.

Option Strict On

Module Example

  Sub Main()
    
    Dim array(5) As Integer

    array(0) = 3
    array(1) = 2
    array(2) = 1
    array(3) = 5
    array(4) = 6

    For i As Integer = 0 To array.Length-1
      Console.WriteLine(array(i))
    Next

  End Sub

End Module

We declare and initialize a numerical array. The contents of the array are printed to the console.

Dim array(5) As Integer

Here we declare an array which contains five elements. All elements are integers.

array(0) = 3
array(1) = 2
...

We initialize the array with some data. This is assignment initialization. The indexes are in the parentheses. Number 3 is going to be the first element of the array, 2 the second.

For i As Integer = 0 To array.Length-1
  Console.WriteLine(array(i))
Next

We go through the array and print its elements. An array has a Length property, which gives the number of elements in the array. Since arrays are zero based, the indexes are 0..length-1.

We can declare and initialize an array in one statement.

Option Strict On

Module Example

  Sub Main()
    
    Dim array() As Integer = { _
      2, 4, 5, 6, 7, 3, 2 }

    For Each i As Integer In array
      Console.WriteLine(i)
    Next

  End Sub

End Module

This is a modified version of the previous program.

Dim array() As Integer = { _
  2, 4, 5, 6, 7, 3, 2 }

An array is declared and initialized in one step. The elements are specified in the curly brackets. We did not specify the length of the array. The compiler will do it for us.

For Each i As Integer In array
  Console.WriteLine(i)
Next

We use the For Each keyword to traverse the array and print its contents.

The bounds of an array

Visual Basic has two functions for getting the bounds of an array. The LBound() function returns the lowest available subscript for the indicated dimension of an array. The UBound() function returns the highest available subscript for the indicated dimension of an array. So far we have worked with one dimensional arrays.

Option Strict On

Module Example

  Dim n1 As Integer
  Dim n2 As Integer

  Sub Main()
    
    Dim names() As String = { "Jane", "Lucy", _
      "Timea", "Beky", "Lenka"}

    n1 = LBound(names)
    n2 = UBound(names)

    Console.WriteLine(n1)
    Console.WriteLine(n2)

    For i As Integer = n1 To n2
      Console.WriteLine(names(i))
    Next

  End Sub

End Module

We have an array of names. We calculate and work with the lower and upper bound of that array.

n1 = LBound(names)
n2 = UBound(names)

The n1 is the lowest index, the n2 the highest index in the names array.

For i As Integer = n1 To n2
  Console.WriteLine(names(i))
Next

We examine the array using both the lower and upper bounds of the array.

$ ./bounds.exe 
0
4
Jane
Lucy
Timea
Beky
Lenka

Output of the example.

Array dimensions

So far, we have worked with one dimensional arrays. The number of indexes needed to specify an element is called the dimension, or rank of the array.

We will work with two dimensional array.

Option Strict On

Module Example

  Sub Main()
    
    Dim numbers(,) As Integer = { {2, 1}, {3, 5}, _
      {4, 4}, {7, 2}, {0, 0} }

    For i As Integer = 0 To UBound(numbers, 1)
      For j As Integer = 0 To UBound(numbers, 2)
        Console.Write(CStr(numbers(i, j)) + " ")
      Next j
      Console.Write(vbNewLine)
    Next i

  End Sub

End Module

If we need two indexes to access an element in an array, than we have a two dimensional array.

Dim numbers(,) As Integer = { {2, 1}, {3, 5}, _
  {4, 4}, {7, 2}, {0, 0} }

We declare and initialize a two dimensional array in one statement. Note the comma inside the parentheses following the name of the array.

For i As Integer = 0 To UBound(numbers, 1)
  For j As Integer = 0 To UBound(numbers, 2)
    Console.Write(CStr(numbers(i, j)) + " ")
  Next j
  Console.Write(vbNewLine)
Next i

We need two loops to get the data from the two dimensional array. The UBound() function has an optional second parameter, rank. It is a dimension for which we retrieve the highest index. If the rank is omitted, the 1 dimension is assumed.

$ ./twodimensions.exe 
2 1 
3 5 
4 4 
7 2 
0 0 

Output of the code example.

Next we will work with a three dimensional array.

Option Strict On

Module Example

  Sub Main()
    
    Dim i As Integer
    Dim j As Integer
    Dim k As Integer

    Dim nums(,,) As Integer = { _
      {{12, 2, 8}}, _
      {{14, 5, 2}}, _
      {{3, 26, 9}}, _
      {{4, 11, 2}} _
    }

    For i = 0 To UBound(nums, 1)
      For j = 0 To UBound(nums, 2)
        For k = 0 To UBound(nums, 3) 
          Console.Write(CStr(nums(i, j, k)) + " ")
        Next k
      Next j   
      Console.Write(vbNewLine)     
    Next i

  End Sub

End Module

We have a numerical three dimensional array. Again, we initialize the array with numbers and print them to the terminal.

Dim nums(,,) As Integer = { _
  {{12, 2, 8}}, _
  {{14, 5, 2}}, _
  {{3, 26, 9}}, _
  {{4, 11, 2}} _
}

There is another comma between the parentheses on the left side and additional curly brackets on the right side.

For k = 0 To UBound(nums, 3) 
  Console.Write(CStr(nums(i, j, k)) + " ")
Next k

This loop goes through the third dimension. We use three indexes to retrieve the value from the array.

$ ./3darray.exe 
12 2 8 
14 5 2 
3 26 9 
4 11 2 

We print the contents of the three dimensional array to the console.

There is a Rank() function, which gives the number of dimensions of an array.

Option Strict On

Module Example

  Sub Main()
    
    Dim array1() As Integer = {1, 2}
    Dim array2(,) As Integer = { { 1 }, { 2 } }
    Dim array3(, ,) As Integer = { { { 1, 2 }, { 2, 1 } } } 

    Console.WriteLine(array1.Rank())
    Console.WriteLine(array2.Rank())
    Console.WriteLine(array3.Rank())

  End Sub

End Module

We have three arrays. We use the Rank() function to get the number of dimensions for each of them.

Console.WriteLine(array1.Rank())

Here we get the rank for the first array.

Jagged arrays

Arrays that have elements of the same size are called rectangular arrays. In contrast, arrays which have elements of different size are called jagged arrays. Jagged arrays are declared and initialized differently.

Option Strict On

Module Example

  Sub Main()
  
    Dim jagged As Integer()() = New Integer(4)() {}

    jagged(0) = New Integer() {1}
    jagged(1) = New Integer() {3, 4}
    jagged(2) = New Integer() {5, 6, 7}
    jagged(3) = New Integer() {5, 6}
    jagged(4) = New Integer() {9}


    For i As Integer = 0 To jagged.GetUpperBound(0)
      For j As Integer = 0 To jagged(i).GetUpperBound(0)
        Console.Write(jagged(i)(j) & " ")
      Next

      Console.Write(vbNewLine)
    Next

  End Sub

End Module

This is an example of a jagged array.

Dim jagged As Integer()() = New Integer(4)() {}

This is a declaration of a jagged array. We have an array of arrays. More specifically, we have declared an array to have five arrays of Integer data type.

jagged(0) = New Integer() {1}
jagged(1) = New Integer() {3, 4}
...

Each of the arrays must be individually initialized.

Console.Write(jagged(i)(j) & " ")

Unlike in rectangular arrays, each index is surrounded by parentheses.

Array methods

There are various methods for working with arrays. These methods can be used for retrieving, modifying data, sorting, copying, searching data. These methods that we use are static methods of the Array class or member methods of the array objects.

Option Strict On

Module Example

  Sub Main()
    
    Dim names() As String = {"Jane", "Frank", "Alice", "Tom" }

    Array.Sort(names)

    For Each el As String In names
      Console.Write(el + " ")
    Next

    Console.Write(vbNewLine)

    Array.Reverse(names)

    For Each el As String In names
      Console.Write(el + " ")
    Next

    Console.Write(vbNewLine)

  End Sub

End Module

In this example, we sort the data.

Dim names() As String = {"Jane", "Frank", "Alice", "Tom" }

We have an array of strings.

Array.Sort(names)

The Sort() method sorts the data alphabetically.

Array.Reverse(names)

The Reverse() method reverses the sequence of the elements in the entire one-dimensional array.

$ ./sorting.exe 
Alice Frank Jane Tom 
Tom Jane Frank Alice

We have ordered the names in ascending and descending order.

The following example uses SeValue() , GetValue() , IndexOf() , Copy() and Clear() methods.

Option Strict On

Module Example

  Dim names() As String = {"Jane", "Frank", "Alice", "Tom" }
  Dim girls(0 To 3) As String

  Sub Main()

    names.SetValue("Beky", 1)
    names.SetValue("Erzebeth", 3)

    Console.WriteLine(names.GetValue(1))
    Console.WriteLine(names.GetValue(3))

    Console.WriteLine(Array.IndexOf(names, "Erzebeth"))

    Array.Copy(names, girls, names.Length)

    For Each el As String In girls
      Console.Write(el + " ")
    Next     

    Console.Write(vbNewLine)

    Array.Clear(names, 0, 2)

    For Each el As String In names
      Console.Write(el + " ")
    Next

    Console.Write(vbNewLine)

  End Sub

End Module

This example introduces additional methods.

Dim girls(0 To 3) As String

Yet another way to declare an array.

names.SetValue("Beky", 1)
names.SetValue("Erzebeth", 3)

The SetValue() sets a value for a specific index in the array.

Console.WriteLine(names.GetValue(1))
Console.WriteLine(names.GetValue(3))

We retrieve the values from the array with the GetValue() method.

Console.WriteLine(Array.IndexOf(names, "Erzebeth"))

The IndexOf() method returns an index for the first occurrence of a specific value.

Array.Copy(names, girls, names.Length)

The Copy() method copies values from the source array to the destination array. The first parameter is the source array, the second is the destination array. The third parameter is the length; it specifies the number of elements to copy.

Array.Clear(names, 0, 2)

The Clear() method clears elements from the array. It takes three parameters, the array, the start index and the number of elements from the index to clear.

In this part of the Visual Basic tutorial, we worked with arrays. We described various types of arrays and methods to work with them.