Passing Two Dimensional Array to Function

Introduction.

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Coming back to our VBA lessons, last week we have briefly touched on the topic of passing Arrays as Parameter to Function ByRef method.  We were able to work with the singly dimensioned Array in its original location within the called function, to sort the values in descending order.  For this example, we have loaded the array with values for only five elements, but the array can have many rows and columns of values.

The Re-Dimension (ReDim) Statement.

An Array can re-dimension, for more rows or fewer rows later on in the program more than once, if we cannot determine the length of the array in advance. In that case, you should not specify the number of elements in advance in the initial Dimension Statement.

Example:

'Cannot Re-dimension pre-defined Arrays
.
Dim Products(1 to 5) as String
.
or
.
Dim Products(5) as String'The number of elements are predefined

'Re-dimension this Array later for required  
'Number of elements, not known in advance. 
.
Dim Products() as String
.
'Re-Dimension the Array for required number of elements
'Remember the array index numbers will be 0 to 4, total 5 elements
ReDim Products(5) As String
'
'OR
'In this case Array Index Number Range 1 to 5
ReDim Product(1 to 5) As String

'later on in the program
'all the values assigned to first 5 elements will be lost.
.
ReDim Products(7) As String 
.
or
.
ReDim Products(Ubound(Products)+2) As String
.
'To preserve the values already assigned to first 5 elements
.
ReDim Preserve Products(7) As String

Note:

The important point to note here is that the ReDimension should take place in the calling program itself, if the need arises in the called function, before passing the Array to the called program.  Even though the Array is passed to the called function ByRef and we are able to work with the passed variable directly, we cannot re-dimension the array to increase/decrease the number of elements in the array, from within the called function.

Two-Dimension Array as Function Argument.

Now, that we are aware of the limitation of the array when passed to the called function, we will try to pass a two-dimensional array of Sales data to a function and print the values in the Debug Window.  The Sales data array has the following values in a record:

1. Product Name - Text
2. Quantity  - Integer
3. Unit Price – Double
4. Total Value  - Double (will be calculated in the called function)

The sales record shows that the data fields have different data types.  To pass values for each field separately to the called function, we need four different array Variables with different data types (1. The String data type for Product-Name, 2. Integer for Quantity, 3. Unit Price & 4. Total Price with Double precision number) and load each field data into separate Array Variables.

We are going to do it differently here.  We will be using only one Variable to pass all four field values to the called function.  We will define a single Variable as a two-dimensional Array of Variant data types, with four rows (each row represents a single record) and four columns (each column is a field).

The Variant Data Type.

We are not storing the above column names anywhere in the array and it is assumed that the first column is Product name, the next column to the right of the first one is Quantity, the next column is Unit Price and the last column is Total Price.  Since the Variant Data Type variable has a peculiar behavior, the data type of the cell changes automatically to match the data type assigned to it.

Before writing it as a complete function, we will look at the dimension statement and how the sales values are assigned to each element of the array. 

' variant Variable can hold different data types in each element 
Dim Product(4,4) as Variant 
'
Product(0, 0) = "Hard Disk": Product(0, 1) = 5: Product(0, 2) = 125.5: Product(0, 3) = 0

Product(1, 0) = "Keyboard": Product(1, 1) = 2: Product(1, 2) = 25.25: Product(1, 3) = 0

Product(2, 0) = "Mouse": Product(2, 1) = 3: Product(2, 2) = 13.75: Product(2, 3) = 0

Product(3, 0) = "DVD Writer": Product(3, 1) = 10: Product(3, 2) = 30: Product(3, 3) = 0

In the above example, we have only four records (or four rows or lines of data) in the Table.  There are four fields (four columns) in each record.  Each cell is numbered with two numbers (row index number, column index number), separated by a comma.  The left-side number is the row index number of the column and the number to the right side of the comma is the column index number.  Both number range is 0 to 3 (4 rows and 4 columns).  The first column (column index 0) is Product Name, 2nd Column  (column index 1) Quantity, 3rd Column (index number 2) Unit Price and the last one is (index number 3) Total Value, which will be calculated and assigned later.

The entire array of these values can be passed to a function as the ByRef parameter and we can work with the array directly from within the called function.  If you are new to two-dimensional arrays, it will be a little confusing at first to comprehend the arrangement of values and how to address each cell to work with it.   This becomes more difficult when there are calculations involving cells of the same row. 

We have a better way to deal with this problem with User-Defined Variables.  Yes, you heard me correctly, we can define our own Variable Type,  besides the built-in variables with default data types.  We will explore this topic further next week and I am sure you will be happier with this new idea, after struggling with these rows and columns set up.  Believe me, this is a very powerful feature once you are familiar with these kinds of data arrangements.  You can work with 5 rows, 500 rows, or 5000 rows with the same statements in the function.

Create the Product List Data.

Public Function ProdList()
Dim Products(4, 4) As Variant
Dim j As Integer, k As Integer, stridx As String
' 0 = Description
' 1 = Quantity
' 2 = Unit Price
' 3 = Total Price to be calculated
'Array elements index numbers are 0 to 3
For j = 0 To 3
 For k = 0 To 3
    stridx = "(" & j & "," & k & ")"
    Select Case k
        Case 0
          Products(j, k) = InputBox("Product Name" & stridx)
        Case 1
          Products(j, k) = InputBox("Quantity" & stridx)
        Case 2
          Products(j, k) = InputBox("Unit Price" & stridx)
        Case 3
          Products(j, k) = 0 'total value will be calculated
    End Select
    Next k
Next j

Call ProdPrint(Products)

End Function

VBA Code Line by Line

We have defined the Products variable as a Variant data type with 4 rows, and 4 columns for assigning values of different data types in them.   The next line sets up three more variables: j & k as a control variable for For … Next loops, the variable stridx for building a string to display the index numbers of cells when displayed in the InputBox() function Prompt text.

Two nested For … Next loops are set up to control the Variable index numbers of rows and column values.  The outer loop controls the row number and the inner loop with the k control variable is used for the column index number.

Next, we used the Select Case ... End Select statements to run several other statements depending on the value in the control variable j. If the value in variable k=0 (and j=0) then the Inputbox() function runs below the Case 0 tests and gets the Product Name and assigns it to the Products(0,0) cell.  When k=1 then the InputBox() gets the value of the Quantity and assigns it to the Products(0,1) cell. When k=2 gets Unit Price and in the next step assigns Products(0,3)=0. The outer loop with the control variable runs only once with zero value as the row index number.

This action repeats 3 more times for the outer For…Next loop to control the row index number and each time the inner For … Next loop runs four times to control the column numbers to get values from the User for each cell for the row number in the j control variable.

The Output Function ProdPrint().

When control comes out of the loop the ProductPrint() Function is called by passing the Products variable as a parameter to the function.

Public Function ProdPrint(List As Variant)
Dim j As Integer, k As Integer

'Ubound() function will get the
'total rows in the array - first value in the Dim statement
For j = 0 To UBound(List, 1) - 1
      List(j, 3) = List(j, 1) * List(j, 2)
    For k = 0 To UBound(List, 2) - 1 'get second value in Dim statement
        Debug.Print List(j, k),
    Next k: Debug.Print
Next j

End Function

The ProductPrint() function takes the Products Array's location address (ByRef) method. If you omit the ByVal or ByRef keyword before the Parameter variable it assumes that Variable List holds the location reference of the Products (parameter passed ByRef).

As in the earlier program, two integer variables j & k  are defined as control variables for outer and inner For … Next loops.  We need these For … Next loops to control the index numbers (rows & columns) to access each element of the array.  The starting value of the Loop is 0 but to calculate the end value we have used another function Ubound() (get Upper Boundary) value of the Array dimension.  In the first program, we have written the control value as 0 to 3.  Here also we could do that, but here we have used the Ubound() function to find the row and column numbers. This will calculate the Array size correctly if the Array size is changed through ReDim statements.

Usage UBound() Function to get Two-Dimension Index Numbers.

UBound(Array,1)

The Ubound(List, 1) gets the number of rows to value, which is 4. But the row index numbers start from 0 in memory so we have used index numbers 0 to 3 in the For … Next loop. The second value 1 in the bracket of the Ubound() function asks for the number of rows in the array.  Since the row index number starts from 0 we are subtracting 1 from the number of row values (4-1).

UBound(Array,2)

The UBound(List, 2) gets the number of column values.  The second parameter value is optional, if it is omitted, it will only get the row value.  If the variable is a singly dimensioned array, then the second value is never used.

The statement immediately after the first For … Next loop ‘List(j, 3) = List(j, 1) * List(j, 2)’ calculates the Total Price of each item and assigns it to the rightmost cell before printing the values of the Sales record item within the next For…Next loop, on the debug window.

Controlling the Print-Head

The comma at the end of the Debug.Print statement positions the next item in the 14th column on the same line, after printing the earlier item.

The empty Debug.Print statement, immediately after the inner Next statement without a comma at the end brings the print control back to the first column of the next line, positions correctly to start printing the next Sales Record.

If we place a semi-colon (;) at the end of the Debug.Print statement the print-head positions to the next character position, without leaving any space between the items printed.

Next week we will explore the User-Defined Variable with the mixed data type. We can give appropriate names for each element of the array rather than assuming names as we did in the above examples. I am sure it will be very interesting to compare the difficulty we had in memorizing each array element's logical name according to its array position.

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