How to initialize a multidimensional array in VB.NET - vb.net

Question

I am trying to initialize a multidimensional array. Here is my syntax; this does not create errors but it does not store all values either. Although it correctly prints out all records in this snippet,
dFirstWeek = CDate(FirstWeek)
dFirstWeek = DateAdd(DateInterval.WeekOfYear, -1, dFirstWeek)
Dim dFirstDay As Date
Dim arrWeekYear(5000, 1) As Date
Dim i As Integer = 0
Dim j As Integer = 0
dFirstDay = dFirstDay.AddDays(1)
While dFirstWeek <= dLastWeek
dFirstDay = dFirstWeek
dFirstWeek = dFirstWeek.AddDays(7)
While dFirstDay < dFirstWeek
arrWeekYear(i, j) = (dFirstWeek)
arrWeekYear(i, j + 1) = (dFirstDay)
Response.Write(arrWeekYear(i, j).ToString("d"))
Response.Write(" ;")
Response.Write(arrWeekYear(i, j + 1).ToString("d"))
Response.Write("<br>")
dFirstDay = dFirstDay.AddDays(1)
j = 0
End While
i = i + 1
End While
later in this code, I try to reprint this array as follows:
i = 0
j = 0
Dim k As Integer = 0
'Response.Write(arrWeekYear.GetLength(0))
While k < arrWeekYear.GetLength(0) - 2
Response.Write(arrWeekYear(i, j).ToString("d"))
Response.Write(" ;")
Response.Write(arrWeekYear(i, j + 1).ToString("d"))
Response.Write("<br>")
j = 0
i = i + 1
k = k + 1
End While
but this time, only one "j" record appears per "i" record. Why is this? And then after these few records, many dates resembling null dates appear: "1/1/0001 "
So why do all records appear in upper section, but not from lower? Did I insert values wrongly into this array? And it does not have to have fixed number of rows, just a fixed number of columns.

Answer 1

Dim arrWeekYear(5000, 1) As Date
That’s a multi-dimensional array all right, but the second dimension only has a size of 2! And you access it via j, which is always 0 in your code. That makes no sense. Is that really what you want? I suggest you use a data structure inside your array instead of a multi-dimensional array.
In fact, you almost never want to use a multi-dimensional array. At all. Complex objects are almost always more appropriate. The only real exception is when you actually want to store a mathematical matrix.

Answer 2

Increment i inside the inner loop, rather than inside the outer loop.
And even simpler code (requires visual studio 2010):
Dim baseDate As Datetime = Convert.ToDatetime(FirstWeek).AddDays(-7)
For Each item In Enumerable.Range(0, (dLastWeek - baseDate).TotalDays / 7) _
.Select(Function(i) New DateTime() _
{baseDate.AddDays(i*7), baseDate.AddDays(i*7 + 7) })
Response.Write(string.Format("{0:d} ;{1:d}<br/>", item(0), item(1)))
Next item
And since Response.Write() is frowned upon in asp.net, you can take this a step further and assign the Enumerable.Range() call as the datasource for an asp:repeater control, if you're using webforms rather than mvc.

Answer 3

In the first piece you fill the array writing 7 times a value in the same array line.
In a test (from 01/01/2011 to 03/03/2011) the first 21 assignments are:
i | j | value | j+1 | value
0 | 0 | 01/01/2011 | 1 | 25/12/2010
0 | 0 | 01/01/2011 | 1 | 26/12/2010
0 | 0 | 01/01/2011 | 1 | 27/12/2010
0 | 0 | 01/01/2011 | 1 | 28/12/2010
0 | 0 | 01/01/2011 | 1 | 29/12/2010
0 | 0 | 01/01/2011 | 1 | 30/12/2010
0 | 0 | 01/01/2011 | 1 | 31/12/2010 final value in array (0,0) and (0,1)
1 | 0 | 08/01/2011 | 1 | 01/01/2011
1 | 0 | 08/01/2011 | 1 | 02/01/2011
1 | 0 | 08/01/2011 | 1 | 03/01/2011
1 | 0 | 08/01/2011 | 1 | 04/01/2011
1 | 0 | 08/01/2011 | 1 | 05/01/2011
1 | 0 | 08/01/2011 | 1 | 06/01/2011
1 | 0 | 08/01/2011 | 1 | 07/01/2011 final value in array (1,0) and 1,1)
2 | 0 | 15/01/2011 | 1 | 08/01/2011
2 | 0 | 15/01/2011 | 1 | 09/01/2011
2 | 0 | 15/01/2011 | 1 | 10/01/2011
2 | 0 | 15/01/2011 | 1 | 11/01/2011
2 | 0 | 15/01/2011 | 1 | 12/01/2011
2 | 0 | 15/01/2011 | 1 | 13/01/2011
2 | 0 | 15/01/2011 | 1 | 14/01/2011 final value in array (2,0) and (2,1)
etc.
In the 2nd part you get the values written :
i | j | value | j+1 | value
0 | 0 | 01/01/2011 | 1 | 31/12/2010
1 | 0 | 08/01/2011 | 1 | 07/01/2011
2 | 0 | 15/01/2011 | 1 | 14/01/2011
3 | 0 | 22/01/2011 | 1 | 21/01/2011
4 | 0 | 29/01/2011 | 1 | 28/01/2011
5 | 0 | 05/02/2011 | 1 | 04/02/2011
6 | 0 | 12/02/2011 | 1 | 11/02/2011
7 | 0 | 19/02/2011 | 1 | 18/02/2011
8 | 0 | 26/02/2011 | 1 | 25/02/2011
9 | 0 | 05/03/2011 | 1 | 04/03/2011
10 | 0 | 01/01/0001 | 1 | 01/01/0001
and this is the value in the rest of the array.
I think you forgot to increment some value in part 1?!?