Visual Basic 2017 Lesson 10: Working with Arrays

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10.1 The Concept of Array

In this lesson, we shall learn how to work with arrays in Visual Basic 2017. By definition, an array is a variable with a single name that represents many different items. To deal with a single item, we only need to declare one variable. However, in dealing with multiple items of similar type, we need to declare an array of variables.

For example, if we need to enter one hundred names, it is difficult to declare 100 different names. Besides, if we want to process those data that involves decision making, we might have to use hundreds of if…then statements, this is a waste of time and efforts. Therefore, instead of declaring one hundred different variables, we need to declare only one array. We differentiate each item in the array by using subscript, the index value of each item, for example, name(1), name(2), name(3) …….etc. , makes declaring variables more two-dimensional




An array in Visual Basic 2017 is a table of items that is made up of rows and columns. The way to reference an element in a one dimensional array is ArrayName(x), where x is the index or position number of the element. The way to reference an element in a two dimensional array is ArrayName(x,y) , where (x,y) is the index or position number of the element. Usually it is sufficient to use one dimensional and two dimensional array, you only need to use higher dimensional arrays if you need to deal with more complex problems. Let me illustrate the the arrays with tables.

10.2 Dimension of an Array

In Visual Basic 2017, an array can be one dimensional or multidimensional. One dimensional array is like a list of items or a table that consists of one row of items or one column of items.

Table 10.1: One Dimensional Array

Student Name Name(0) Name(1) Name(2) Name(3) Name(4) Name(5) Name(6)

Table 10.2: Two Dimensional Array

A two dimensional array is like a list of items or a table that consists of n row of items and m column of items. The following example is a 4×4 array.

Column1 Column2 Column3 Column4
Row1 Name(0,0) Name(0,1) Name(0,2) Name(0,3)
Row2 Name(1,0) Name(1,1) Name(1,2) Name(1,3)
Row3 Name(2,0) Name(2,1) Name(2,2) Name(2,3)
Row4 Name(3,0) Name(3,1) Name(3,2) Name(3,3)


10.2 Declaring Arrays

In Visual Basic 2017 , we can use Public or Dim statement to declare an array just as the way we declare a single variable. The Public statement declares an array that can be used throughout an application while the Dim statement declare an array that could be used only in a local procedure or module.

10.2.1 Declaring One Dimensional Array

The syntax to declare a one dimensional array is as follows:

Dim arrayName(n) as dataType

where n indicates the last index(or subscript) in the array. Please note that n does not indicate the number of elements in the array, it is one less than the number of elements (n-1) because the first element is always the zeroth element. The first element is arrayName(0), the second element is arrayName(1), the third element is arrayName(2) and so on. The number of elements in an array is also known as length, we can retrieve the length of an array using the syntax arrayName.length 

For example,

Dim CusName(10) as String

will declare an array that consists of  11 elements starting from CusName(0) through to CusName(10)

To find out the length of the array, you can write the following code:

Example 10.1

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim CusName(10) As String
MsgBox(CusName.Length)
End Sub

Running the program will produce a message box that displays the length of the array i.e 11, as shown in Figure 10.1

vb2013_figure10.1

Figure 10.1

You might also declare an array with a non-zero starting index by initialize an index value other than zero, as follows:

Dim arrayname As DataType()

arrayName=New String(){1,2,3,....,n)

This array will consists of n elements, starting with arrayName(1)

 Example 10.2

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim CusName As String()
CusName = New String() {1, 2, 3}
MsgBox(CusName.Length)
End Sub

The message box will display the length as 3

 

Example 10.3

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim num As Integer
Dim CusName(5) As String
For num = 0 To 5
CusName(num) = InputBox("Enter the customer name", "Enter Name")
ListBox1.Items.Add(CusName(num))
Next
End Sub

This program will prompt the user to enter names in an input box for a total of 6 times and the names will be entered into a list box, as shown in Figure 10.2 and Figure 10.3

vb2013_figure10.3

 Figure 10.3 

vb2013_figure10.4

Figure 10.4 

10.2.2 Declaring Two Dimensional Array

The statement to declare a two dimensional array is as follow:

Dim ArrayName(m,n) as dataType

where m and n indicate the last indices in the array. The number of elements or the length of the array is (m+1)x(n+1)

Example 10.4

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Dim CusName(5,6) As String
MsgBox(CusName.Length)
End Sub

Running the program and the message box will display a length of 42, as shown in Figure 10.5

vb2013_figure10.2

Figure 10.5

Example 10.5

In this example, we want to summarize the first half-yearly sales volume for four products. Therefore, we declare a two dimension array as follows:

Dim saleVol(4, 6) As Integer
Besides that, we want to display the output in a table form. Therefore, we use a list box. We named the list box listVolume. The syntax to populate the list box is Listbox.Items.Add.

The Code

Private Sub BtnAdd_Click(sender As Object, e As EventArgs) Handles BtnAdd.Click
        Dim prod, mth As Integer ' prod is product and mth is month
        Dim saleVol(4, 6) As Integer
        Const j = 1
        ListVolume.Items.Add(vbTab & "January" & vbTab & "February" & vbTab & "March" _
& vbTab & "Apr" & vbTab & "May" & vbTab & "June")
        ListVolume.Items.Add(vbTab & "____________________________________________")
        For prod = 1 To 4
            For mth = 1 To 6
                saleVol(prod, mth) = InputBox("Enter the sale volume for" & " " & "product" & " " & prod & " " & "month" & " " & mth)

            Next mth
        Next prod

        For i = 1 To 4

            ListVolume.Items.Add("Product" & "" & i & vbTab & saleVol(i, j) & vbTab & saleVol(i, j + 1) & vbTab & saleVol(i, j + 2) _
& vbTab & saleVol(i, j + 3) & vbTab & saleVol(i, j + 4) & vbTab & saleVol(i, j + 5))

        Next i

    End Sub

*Notice that we have omitted the elements saleVol(0,m), where m=0,1,2,3,4,5,6 and saleVol(n,0) where n=0,1,2,3,4. This is done for easy reading of the code.

The Output

Figure 10.6

16.3 Dynamic Array

So far we have learned how to define the number of elements in an array during design time. This type of array is known as a static array. However, the problem is sometimes we might not know how many data items we need to store during run time. In this case, we need to use dynamic array where the number of elements will be decided during run time. In VB2017, the dynamic array can be resized when the program is executing. The first step in declaring a dynamic array is by using the Dim statement without specifying the dimension list, as follows:

Dim myArray()

Then at run time we can specify the actual array size using the ReDim statement,  as follows:

ReDim myArray(n)
* n =array size
You can also declare a two dimensional array using ReDim statement, as follows:

ReDim myArray(n, m)
*mxn indicates the array size.

Example 10.6

In this example, we want to display the elements of an array in a list box. The size of the array will only be known during run time. It demonstrates the creation of a dynamic array using the ReDim keyword.

The Code

Public Class Form1
    Private Sub BtnDisplay_Click(sender As Object, e As EventArgs) Handles BtnDisplay.Click
        Dim myArray() As Integer
        Dim i, n As Integer
        n = InputBox("Enter the upper bound of array")
        ListBox1.Items.Clear()

        For i = 1 To n
            ReDim myArray(i)
            myArray(i) = i ^ 2
            ListBox1.Items.Add(myArray(i))

        Next

    End Sub
End Class

The Ouitput

Figure 10.6





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