VBA Excel Function Error Runtimeerror 13 - vba

Question

I cannot find the mistake. The error msg gives me "runtime error '13'" data types don't match. The error seems to be in the function "fillcalweeks".
Fillcalweeks should return an array which is filled with start and end dates which are located in a sheet.
Here's my code:
'For every calenderweek we need the start and end dates in an array to produce the timeline
Sub get_cal_weeks()
Dim weeks As Integer, i As Integer, col As String, weekstart As Date, weekend As Date
'start column is D
col = "D"
'get amount of weeks
weeks = countcalweeks()
'populate array calweeks
calweeks = fillcalweeks(weeks)
For i = 0 To weeks
Sheets("Kalenderwochen").Range("E" & i + 1) = calweeks(i, 1)
Next
End Sub
Function fillcalweeks(weeks As Integer) As String()
Dim i As Integer, datestart As Date, dateend As Date, calweek As Integer, returnarray() As String
For i = 0 To weeks
'date start & date end
datestart = Sheets("Kalenderwochen").Range("A" & i + 1).Value
dateend = Sheets("Kalenderwochen").Range("B" & i + 1).Value
calweek = Sheets("Kalenderwochen").Range("C" & i + 1).Value
returnarray(i, 1) = datestart
returnarray(i, 2) = dateend
returnarray(i, 3) = calweek
fillcalweeks = returnarray
Next
End Function
'Counts the calenderweeks in the Kalenderwochen sheet
Function countcalweeks() As Integer
countcalweeks = Sheets("Kalenderwochen").Range("A2").End(xlDown).row
End Function
Thx for the help

Answer 1

You are getting an error on the line calweeks = fillcalweeks(weeks) because you are assigning a String array (the result of the function fillcalweeks to a Variant.
You'll notice you declared every variable except calweeks. Since VBA doesn't have an explicit declaration for this variable it assigns it to a Variant.
To fix the problem, start by putting Option Explicit at the top of every module. When you compile the project, it'll alert you to errors such as these (Debug -> Compile VBA Project). Then all you need to do is declare calweeks as a String().
There is a second problem you have and that is that you are trying to store a Date data type in your String() array within the fillcalweeks. You either need to convert the datestart, dateend and calweek variables to Strings (you can use the VBA.CStr() function to do this) or change the function fillcalweeks to return a Date array.
Finally, you need to declare a size range for the returnarray() within fillcalweeks. VBA needs to know how big this is before it can fill the values. Since you know how many rows there are (its an input to the function) this is as simple as replacing the declaration of returnarray with ReDim returnarray(0 To weeks - 1, 1 to 3) As String. Note you want to dimension the array to weeks - 1 since you have a base of zero not one.
One more error is that when you output back to the worksheet the loop needs to be For i = 0 To weeks - 1 otherwise the array will be out of bounds...

Answer 2

Thx. I found all the mistakes in the code. 1. declaration of calweeks and 2. the array dimension:
'For every calenderweek we need the start and end dates in an array to produce the timeline
Sub get_cal_weeks()
Dim weeks As Integer, i As Integer, col As String, weekstart As Date, weekend As Date, calweeks() As Variant
'start column is D
col = "D"
'get amount of weeks
weeks = countcalweeks()
'populate array calweeks
calweeks = fillcalweeks(weeks)
For i = 0 To weeks
field = i + i + 4
weekstart = calweeks(i, 0)
weekend = calweeks(i, 1)
Cells(5, field) = monetary_calc_week(weekstart, weekend)
Next
End Sub
Function fillcalweeks(weeks As Integer) As Variant()
Dim i As Integer, datestart As Date, dateend As Date, calweek As Integer, arraysize As Integer, returnarray() As Variant
arraysize = 52
weeks = weeks - 2
ReDim Preserve returnarray(arraysize, 3)
For i = 0 To weeks
If i > arraysize Then
arraysize = arraysize * 2
ReDim Preserve returnarray(arraysize, 3)
End If
'date start & date end
datestart = Sheets("Kalenderwochen").Range("A" & i + 2).Value
dateend = Sheets("Kalenderwochen").Range("B" & i + 2).Value
calweek = Sheets("Kalenderwochen").Range("C" & i + 2).Value
returnarray(i, 0) = datestart
returnarray(i, 1) = dateend
returnarray(i, 2) = calweek
Next
fillcalweeks = returnarray
End Function
'Counts the calenderweeks in the Kalenderwochen sheet
Function countcalweeks() As Integer
countcalweeks = Sheets("Kalenderwochen").Range("A2").End(xlDown).row
End Function