Array Tutorial-Part 1
What are variable arrays?
Variable arrays are a collection of variables with the same name that are referenced by an index.
What are control arrays?
Control arrays are a collection of controls with the same name that are referenced by an index.
What are User Defined arrays?
User Defined Arrays are a collection of variables with the same name that are referenced by an index, and that
have multiple pieces of data for each element of the array.
When should I use arrays?
This is a question that only you can answer. By the time you finish reading this tutorial, you should be able
to answer the question yourself.
How do I declare a variable array?
There are many ways to declare a variable array. I will show you several of the methods.
Dim sArray() as String
Dim sArray(10) as String
Dim sArray(1 to 10) as String
Dim sArray(kMaxSize) as String
The four declarations above are all valid declarations for an array. Below are the differences. For simplicity
sake, I declared all the arrays as strings, but you can declare the arrays as any type that you want, including
User Defined, which I will address later.
Dim sArray() as String
This method simply declares sArray to be an array of any size. You will need to ReDim the array
later in code before you can use it. If you are unsure of how much data you are going to be storing, this is
the best method to use. This allows you to dynamically resize the array, larger or smaller, as you need it.
More on ReDim later on.
Dim sArray(10) as String
So, how big is this array? 10 elements, right? Wrong. By default, all arrays are 0 based, unless
specified otherwise. This means that the first element in the array is 0. This gives us 0 to 10 elements. 0 to 10
equals 11 elements total.
Dim sArray(1 to 10) as String
This array is 10 elements long. We specified a starting point when we declared this array. You can
use any starting and ending values you want, however, the beginning element must be less than the ending
element.
Dim sArray(kMaxSize) as String
This array will be however large the constant kMaxSize is. This array will be 0 based, since we did
not specify the starting element. We could have used: Dim sArray(5 to kMaxSize) as String if we had wanted
to start with the 5th element.
First, I will cover a few of the functions that are used with Arrays.
iUpper = UBound(sR) 'UBound retrieves the upper end of the
array
iLower = LBound(sR) 'LBound retrieves the lower end of the
array
ReDim sR(10) 'ReDim adjusts the array size, destroying
existing data
ReDim Preserve sR(10) 'Adjusts the array size, keeping
existing data
How do I declare a User Defined array?
OK, first you need to define the Type.
Public Type MY_ARRAY_TYPE
lValue as Long
sTemp as String
iCount as Integer
End Type
The first line declares the type. It is Public so it can be accessed anywhere in the project. Then next three
lines simply declare the values that are to be used in the type. You can have any almost variable type within
a Type, including other Types. The last line closes the Type. If you are not familiar with Types then you should
read up on them. They can be very useful in VB, especially when dealing with API calls, or arrays.
Now you declare the array like this:
Dim uArray() as MY_ARRAY_TYPE
You can use any of the methods listed for variable arrays for declaring a User Defined array. You can
specify upper and lower bounds, use a constant for the upper and or lower bounds or even make the array
variable length.
How do I declare a Control array?
Well, you do not actually declare a control array. You normally put the control array on the form at design
time.
1. Add a Text box to the form.
2. Name the Text box txtArray
3. Change the Index of the text box to 0. This changes the value from nothing (non-arrayed
control) to 0 (arrayed control)
4. Copy the txtArray control and paste it back to the form.
If you look at the new txtArray control's properties, you will notice that it now has an Index of 1. This is
because there are two elements of the txtArray control array. 0 and 1.
You can also load control arrays at run time, via code. This can be a little complex, but nothing the average
programmer cannot master with a little time and practice. I will cover this topic later during this tutorial.
How do I access my array?
Remember the index we mentioned in the very beginning? Well, here is where you use it.
If you want to access the 1st element in an array, you would use:
Debug.Print sArray(0) 'Prints 'Element 0' in the Immediate window.
Debug.Print uArray(0) 'Prints 'Element 0' in the Immediate window.
Debug.Print txtArray(0) 'Prints 'Element 0' in the Immediate window.
Remember that unless we specified otherwise, the arrays first element is always 0. If you try to access an
index value that does not exist, you get the following error.
Run-time Error '9': Subscript out of range
If you want to assign a value to the array, you would use:
sArray(0) = "My String"
txtArray(0).Text = "My Text"
And for the User Defined, you would use:
uArray(0).lValue = 300
uArray(0).sTemp = "Temp String"
uArray(0).iCount = uArray(0).iCount + 1
How do I change the size of my array after I have declared it?
You use the ReDim statement.
ReDim sArray(5) 'Six elements, erases data that was already in array.
ReDim Preserve sArray(5) 'Six elements, keeps data that was already in the array.
Since we previously declared the array as a String, we do not declare the array as anything this time.
Here is a code example you can paste into the Click event of a form.
Dim sArray(1 To 5) As String
Dim iCount As Integer
For iCount = 1 To 5
sArray(iCount) = "Element " & iCount
Next iCount
Debug.Print sArray(3) 'Prints 'Element 3' in the Immediate window.
ReDim Preserve sArray(1 To 10)
Debug.Print sArray(3) 'Prints 'Element 3' in the Immediate window.
ReDim sArray(1 To 20)
Debug.Print sArray(3) 'Prints an empty line in the Immediate window.
Ok, so now you know how to declare an array, and how to access and assign data to arrays.
When do you
use them?
I will show you several methods where you might want to use an array.
1. You want to store a list of all files within a directory. (Variable Array)
2. You want to store a list of all files within a directory. (User Defined Array)
3. You want to create a bunch of command buttons. (Control Array)
Storing a list of all files within a directory using a Variable Array
OK, enter the following code into the Click event of a form.
Dim sFile As String
Dim sArray() As String
Dim i As Integer
sFile = Dir$("C:\") 'Get first entry
Do Until Len(sFile) = 0 'Loop until we run out (sFile will be empty)
If Not sFile = "." And Not sFile = ".." Then
ReDim Preserve sArray(i)
sArray(i) = sFile 'Display what we found
i = i + 1
End If
sFile = Dir$ 'Get next entry.
Loop
For i = 0 To UBound(sArray) 'Now we have all the files in an array, so..
Debug.Print sArray(i) 'We show them.
Next i
Storing a list of all files within a directory using a User Defined Array
Type MY_ARRAY_TYPE
sFile as String
sExtension as String
End Type
Remember, the Type declaration has to be in the General Declarations section (right after the Option
Explicit). This can not be put into the Form Load event, or anything like that.
Dim sFile As String
Dim sArray() As MY_ARRAY_TYPE
Dim i As Integer
sFile = Dir$("C:\") 'Get first entry
Do Until Len(sFile) = 0 'Loop until we run out (sFile will be empty)
If Not sFile = "." And Not sFile = ".." Then
ReDim Preserve sArray(i)
sArray(i).sFile = sFile 'Display what we found
sArray(i).sExtension = Right$(sFile, 3)
i = i + 1
End If
sFile = Dir$ 'Get next entry.
Loop
For i = 0 To UBound(sArray) 'Now we have all the files in an array, so..
Debug.Print sArray(i).sFile, sArray(i).sExtension 'We show them
Next I
Creating command buttons using a Control Array
1. Start a new VB project.
2. Place a command button on the form.
3. Name the command button cmdArray
4. Set the Index property to 0
5. Paste the following code into the Form, and run the program.
Private Sub Form_Load()
Dim i As Integer
cmdArray(0).Caption = "Command 0"
For i = 1 To 9
Load cmdArray(i)
With cmdArray(i)
.Caption = "Command " & i
.Visible = True
.Top = cmdArray(i - 1).Top + 550
End With
Next i
End Sub
To access the control array, simply reference the index value for the control you want. Paste the code below
into the form.
Private Sub cmdArray_Click(Index As Integer)
Select Case Index
Case 0, 1, 2
MsgBox "You pressed button " & Index, vbOKOnly, "Group 1"
Case 3, 4, 5
MsgBox "You pressed button " & Index, vbOKOnly, "Group 2"
Case 6, 7, 8
MsgBox "You pressed button " & Index, vbOKOnly, "Group 3"
Case 9
MsgBox "You pressed button " & Index, vbOKOnly, "This button is all alone."
End Select
End Sub
If you want to change the property of a command button, then just reference it like you would any other
array element.
cmdArray(3).Caption = "This is command button 3"
Tutorial submitted by:
Eric D. Burdo,
Red-Leif International
VB Programmer and Consultant
http://www.redleif.com
