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: 182 times
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