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Array Basics (FIXED 18-Apr-08)


Array basics for beginners

Original Author: Rde

Code





' There are two areas where arrays can be declared.


' Firstly in the General Declarations section. Arrays declared

' here are seen by all procedures in this form or module:


Private arrayName([intLow To] intHigh) As dataType


' For example:


Private lngArray(2 To 4) As Long


' You can also declare the array as Public, making it visible to

' all forms and modules in the application:


Public arrayName([intLow To] intHigh) As dataType


' For example:


Public strArray(0 To 200) As String


' Secondly, within procedures:


Dim arrayName([intLow To] intHigh) As dataType


' For example:


Dim intArray(0 To 9) As Integer


' You can also specify element size like a string variable:


Dim arrayName([intLow To] intHigh) As dataType * intByteSize


' For example:


Dim strArray(3 To 14) As String * 256


' Also, you can just specify the array length by omitting the

' [intLow To] code shown above. This specifies the upper

' element's index, not neccessarily the arrays length:


Dim ArrayName(intHigh) As dataType


' For example:


Dim intArray(9) As Integer


' This array will be indexed from 0 by default (so the array's

' size will be one greater than intHigh) unless the following

' line is added to the General Declarations section:


Option Base 1




' You can also do this (for single dimensional arrays only):


Dim scores As Variant

scores = Array(81, 49, 80, 71, 92, 66)


' The above scores array will be indexed from 0 unless Option Base 1

' is added to the General Declarations section.




' VB supports static and dynamic arrays. Static arrays are fixed in

' size and can't be changed at runtime, dynamic array sizes can.


' Static arrays are more memory efficient:


Dim array2(10 To 20) As Integer


' Dynamic arrays do not have a size defined when initialized:


Dim array3() As Integer


' You must ReDim a dynamic array to change its size at runtime:


ReDim array3(1 To 4) As Integer


' You can preserve the contents of the array elements when you

' ReDim the array by using the Preserve keyword with ReDim:


ReDim Preserve array3(1 To 9) As Integer


' You can also assign to a dynamic array directly from another

' array without specifying size:


Dim array4() As Integer


array4 = array3


' array4 will now be initialize with the size

' (and element values if any) of array3.




' Visual Basic allows you to use For Each ... Next to enumerate

' the items in an array:


Dim element As Variant

For Each
element In array4()

 
'code to process array elements sequentially

Next


' Because arrays do not have a Count property you can use the

' UBound and LBound methods to establish its length.


' You could use a loop like the following:


For x = LBound(ArrayName()) To UBound(ArrayName())

 
'code to process array items sequentially

Next


' The arrays empty parentheses are not required, so the first

' line of code above could be like this:


For x = LBound(ArrayName) To UBound(ArrayName)


' To establish the length you could also use the following code

' that subtracts the LowerBound value from the UpperBound value,

' then adds one to the result because the array elements include

' both upper and lower, then returns the result As Integer:


Function GetCount(AnyArray As Variant) As Integer

  On
Error Resume Next

  Dim
length As Integer

 
length = UBound(AnyArray) - LBound(AnyArray) + 1

 
GetCount = length             ' + 1 = inclusive

End Function


' If you know the data type of the array you could declare

' the AnyArray argument as that type instead of As Variant

' to improve performance:


Function GetCount(sngArray() As Single) As Integer

  On
Error Resume Next

  Dim
length As Integer

 
length = UBound(sngArray) - LBound(sngArray) + 1

 
GetCount = length             ' + 1 = inclusive

End Function


' Calling the function is as easy as:


intCount = GetCount(myArray())




' Multi-dimensional arrays


' Each dimension of the array must contain the same data type.


' The second-last and last dimensions of a multi-dimensional array

' are normally considered to be a Row and a Column respectively.


Private multiArray(1 To 5, 1 To 3) As Integer


' So for a two dimensional array in VB the dimension (row) is

' defined first, and the number of elements (cols) for each

' dimension defined second:


Public 2DArray(1 To 2, 1 To 8) As Long


' This array is a two dimensional array containing 8 elements

' in each dimension:


Dim i1 As Integer, i2 As Integer

For
i1 = 1 To 2

 
For i2 = 1 To 8

   
2DArray(i1, i2) = "Cell " & CStr(i1) & "," & CStr(i2)

 
Next

Next


' You can also assign arrays to the elements of other arrays to

' create multi-dimensional arrays:


Public Sub CreateMultiArray()

 
Dim intX As Integer ' Declare counter variable


  ' Declare and populate an integer array

 
Dim countersA(1 To 4) As Integer


  For intX = 1 To 4

   
countersA(intX) = intX

 
Next intX


  ' Declare and populate a string array

  Dim countersB(1 To 4) As String


  For intX = 1 To 4

   
countersB(intX) = "hello"

 
Next intX


  ' Declare a new two-member array

  Dim arrX(1 To 2) As Variant


  ' Populate the array with other arrays

  arrX(1) = countersA()

  arrX(2) = countersB()


  ' Display a member of each array

  MsgBox arrX(1)(2)

  MsgBox arrX(2)(3)


End Sub


' To increase the size of an array without losing its current

' values use the Preserve keyword:


ReDim Preserve DynArray(UBound(DynArray) + 1)


' Only the upper bound of the last dimension in a multi-dimensional

' array can be changed when you use the Preserve keyword; if you

' change any of the other dimensions, or the lower bound of the

' last dimension, a run-time error occurs.


' Thus, you can use code like this:


ReDim Preserve Matrix(10, UBound(Matrix, 2) + 1)


' But you cannot use this code:


ReDim Preserve Matrix(UBound(Matrix, 1) + 1, 10)




' Multi-dimensional array demonstration


' The following code can be copied and pasted into the form of

' a new project and after creating three command buttons named

' cmdFill, cmdShow and cmdMulti you can run the program:


Option Explicit


Option Base 1


Private multiArray(1 To 5, 1 To 3) As String

Private
counter As Integer


Private Sub cmdFill_Click()


  Dim idx1 As Integer, idx2 As Integer


  For idx1 = 1 To 5

   
For idx2 = 1 To 3

     
counter = counter + 1

     
multiArray(idx1, idx2) = "Cell " & CStr(counter)

   
Next

  Next


End Sub


Private Sub cmdShow_Click()


  Me.Refresh

  CurrentY
= 100

  Print " Dim multiarray(1 To 5, 1 To 3) As String"

  CurrentY = 400


  Dim idx1 As Integer, idx2 As Integer


  For idx1 = 1 To 5

    For idx2 = 1 To 3

      Print "  multiarray(" & _

        CStr(idx1) & "," & CStr(idx2) & ") = " & _

        Chr
(34) & multiArray(idx1, idx2) & Chr(34)

    Next

  Next


End Sub


Private Sub cmdMulti_Click()

  Dim intX As Integer ' Declare counter variable


  ' Declare and populate an integer array

  Dim countersA(4) As Integer


  For intX = 1 To 4

    countersA(intX) = intX

  Next intX


  ' Declare and populate a string array

  Dim countersB(4) As String


  For intX = 1 To 4

    countersB(intX) = "hello"

  Next intX


  ' Declare a new two-member array

  Dim arrX(1 To 2) As Variant


  ' Populate the array with other arrays

  arrX(1) = countersA()

  arrX(2) = countersB()


  ' Display a member of each array

  MsgBox arrX(1)(2)

  MsgBox arrX(2)(3)

End Sub




About this post

Posted: 2002-06-01
By: ArchiveBot
Viewed: 183 times

Categories

Visual Basic 6

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