Subtracting Variants - excel

Question

I am having trouble getting Variants to subtract. I am pulling data from a spreadsheet and if one cell states a phrase then I need the code to subtract one cell from another. If the cell does not state a phrase then I need it to copy one cell to another. I can get the code to run but nothing happens.
Private Sub CommandButton1_Click()
Dim x As Variant, y As Variant, z As Variant, a As Integer, B As String
'getting values for data
x = Range("D2:D48").Value
y = Range("I2:I48").Value
z = Range("E2:E48").Value
B = "Total ISU Days: "
'The the cells are empty then subtract. This is not what I wanted to do but I can't think of extracting strings from variants.
If IsEmpty(Range("D2:D48").Value) = True Then
a = y - z
End If
Range("N2:N48").Value = a
Range("M2:M48").Value = B
End Sub

Answer 1

x = Range("D2:D48").Value
y = Range("I2:I48").Value
z = Range("E2:E48").Value
A Variant contains metadata about its subtype. In this case, x, y, and z are all arrays of variants.
a = y - z
The right-hand side of this expression simply cannot be evaluated, because {array1} - {array2} means nothing: operators (arithmetic or logical) work off values, not array of values.
What is a supposed to be? It's declared As Integer, so its value is capped at 32,767 (should probably be a Long). If you mean to add up all the values in y and subtract that total from the sum of all values in z, then you need to be more explicit about how you do that - you could use Application[.WorksheetFunction].Sum to add things up:
sumOfY = Application.Sum(Range("I2:I48"))
sumOfZ = Application.Sum(Range("E2:E48"))
a = sumOfY - sumOfZ
And then...
Range("N2:N48").Value = a
That will put the value of a in every single cell in the N2:N48 range - is that really what you mean to do?
Or maybe you meant to do this instead?
Range("N2:N48").Formula = "=IF(D2="""",I2-E2,0)"
That would make each cell in N2:N48 calculate the difference between I and E for each row where D is empty... and there's not really any need for any VBA code to do this.

Answer 2

Let's simplify a bit the task and say that the idea is to substract the values in Range("C1:C6") from the corresponding values in the left - Range("B1:B6"). Then write the corresponding results in column E:
Of course, this would be done only in case that all values in column A are empty. This is one way to do it:
Sub TestMe()
Dim checkNotEmpty As Boolean: checkNotEmpty = False
Dim substractFrom As Range: Set substractFrom = Worksheets(1).Range("B1:B6")
Dim substractTo As Range: Set substractTo = Worksheets(1).Range("C1:C6")
Dim MyCell As Range
Dim result() As Variant
ReDim result(substractFrom.Cells.Count - 1)
Dim areCellsEmpty As Boolean
For Each MyCell In substractFrom
If Len(MyCell) > 0 Then checkNotEmpty = True
Next
Dim i As Long
For i = LBound(result) + 1 To UBound(result) + 1
result(i - 1) = substractFrom.Cells(i) - substractTo.Cells(i)
Next
Worksheets(1).Range("E1").Resize(UBound(result) + 1) = Application.Transpose(result)
End Sub
The code could be improved further, saving all ranges to an Array, but it works quite ok so far.
The part with the +1 and -1 in the For-loop is needed as a workaround:
For i = LBound(result) + 1 To UBound(result) + 1
result(i - 1) = substractFrom.Cells(i) - substractTo.Cells(i)
Next
because the arrays start from index 0, but the Cells in a range start with row 1.
Worksheets(1).Range("E1").Resize(UBound(result) + 1) = Application.Transpose(result) is needed, to write the values of the result array to the column E, without defining the length of the range in E.