Library tutorials & articles
Arrays
James first started this website when learning Visual Basic back in 1999 whilst studying his GCSEs. The site grew steadily over the years while being run as a hobby - to a regular monthly audience ...
Dynamic Arrays
When using arrays you must be careful not to consume too much memory. For example
Dim MyArray (10000) As Long
Because each element is declared as long, and a long variable occupies 4 bytes of memory, the MyArray requires 40 004 (10 001 x4) bytes of memory. This may not sound like much, but when you have 10 such arrays in your program these arrays consume 400 040 (40 004 x 10) bytes of memory. Therefore, it is wise to always try to set the size of your arrays to the minimum your program requires. Sometimes, however, it is only possible to detemine this during runtime. In these cases you can use the ReDim statement to change the size of an array. An array that changes its size during runtime is called a dynamic array.
When you declare a dynamic array, you do not declare it like a fixed array. When you declare a dynamic array the size is not specified. Instead you use the following syntax:
Dim ArrayName() As DataType
Dim is the scope of the array. If you declare it in a Form, use Dim, if you declare it in a Module and you want every procedure to access it, declare it as Global, otherwise use Public. If you declare the array in a procedure use Dim. ArrayName is the name of the array. DataType is a valid datatype. Normally Integer (-32 768 to 32 767), String (A string of characters), Boolean (True or False).
You then use the ReDim statement in your procedures or functions, using the following syntax:
ReDim ArrayName(LowerValue To HigherValue)
In fact, it is almost identical to a normal declaration for a fixed array, except that 1), it is not a declaration, as it is executed at runtime, 2) it uses ReDim, and 3) there is no datatype declaration (this cannot be changed).
So, the following code declares a dynamic array called gArray, and then sets the size during runtime:
Dim sStringArray() As String
Sub Form1_Load()
' Initialise array
ReDim sStringArray(1 To 10)
End Sub
This code assigns 10 elements to gArray when Form1 loads. Note: When using dynamic arrays, you must set the size of an array using the ReDim statement, before filling the array.
However, when using the ReDim statement, any values already in the array (if it has been resized previously), will be deleted. In some cases, this is not what you would want! So, you use the Preserve keyword:
ReDim Preserve ArrayName(LowerValue To HigherValue)
If the array has grown, there will be a number of blank array spaces at the end of the array. If the array has shrunk, you will lose the end items.
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I'm a bit confuse. I would like user to insert how many data they want to put in the array.
When I declare the array like this
Dim subjArr( ) As DataType
How should I write the code so array size is according to user input. This is the code for user to insert how many records should be inserted.
Dim SubArr() As DataType
Dim subjNo As String
subjNo = InputBox("Enter the no of subjects to calculate: ")
MsgBox (subjNo + " subjects will be calculated")
It would work if you used Dim instead of Const. A constant array is not possible in VB and I really don't see the point. Just use a normal array and make sure that it is not modified.
Thanks James
This is a good Array Tutorial for VB Newbies like me.
These guys have a perfect working example. The randomizer isn't truly random but completely adequate for basic purposes. I couldn't get it to work as a function, but it worked great when I simply used to function code in-line, so I know it works.
http://www.4guysfromrolla.com/webtech/110800-1.shtml
I really just added this in case anyone comes across this in a search as I did
+++++++++++++++
check it: FLEETING IMAGE
How do I make a constant array? When I try "const data(1 to 72) as byte" it doesn't work, where it would if I used Dim rather than const. Also, isn't there some way to set a value to the whole thing? Like with one command making data(1) = 4, data(2) = 7 etc.
No, I believe he means something like this:
Say you had a string array with 6 elements, beginning with zero.
The values were arranged like this:
strArray(0) = "Step 1"
strArray(1) = "Step 2"
strArray(2) = "Step 3"
strArray(3) = "Step 4"
strArray(4) = "Step 5"
strArray(5) = "Step 6"
He wants to randomly arrange the elements' contents, like this:
strArray(0) = "Step 4"
strArray(1) = "Step 3"
strArray(2) = "Step 5"
strArray(3) = "Step 1"
strArray(4) = "Step 6"
strArray(5) = "Step 2"
I hope this is correct, and/or clear.
Are you speaking of randomly pulling one of the values as in say a random name generator?
Can anyone tell me if it's possible to randomly sort the elements in an array?
I'm not familiar to 3d arrays, but could you use something similar to:
I use that to copy 1d arrays.
Not the best piece of code but meh.
Does anyone know a way of transferring the content of an array into another array WITHOUT doing this?:
Public Sub MoveArray()
For Z = 0 To 10
Array2(Z) = Array1(Z)
Next Z
End Sub
I am dealing with some very large (3 dimensional) arrays and the above kind of operation seems a little slow for the user to sit around waiting for. (Especially when it will need to be used in the Undo Function)
Any suggestions will be gratefully received.
couling@fsnet.co.uk">pcouling@fsnet.co.uk
This thread is for discussions of Arrays.