Stored list of array using For Each loop - vb.net

Question

I want to store the "zone_check_value" to a array of string then while inserting into array i will check the array of string if the next value is repeated or have duplicate.
Example.
1st Example
1st loop = zone_check_value = ZD1/01/2014
2nd loop = zone_check_value = ZD1/01/2014
2nd Example
1st loop = zone_check_value = ZD1/01/2014
2nd loop = zone_check_value = ZD2/02/2014
3rd loop = zone_check_value = ZD1/01/2014
Code:
For Each dt As DataTable In xls.Tables
Dim array_of_string as String() 'i want to put the value in here
For Each dr As DataRow In dt.Rows
Dim zone_destination As String = dr(2).ToString
Dim affected_date As String = dr(7).ToString
Dim zone_check_value = zone_destination + affected_date
''''''How can i store zone_check_value in a string array?
Next
Next
EDIT
What if i add select case in my loop? the array_of_string value become NULL. I need to check the value of the current value in array_of_string .
Example Code
For Each dt As DataTable In xls.Tables
Dim array_of_string as String() 'i want to put the value in here
select Case dt.tablename
case "Sheet1"
For Each dr As DataRow In dt.Rows
Dim zone_destination As String = dr(2).ToString
Dim affected_date As String = dr(7).ToString
Dim zone_check_value = zone_destination + affected_date
''''''How can i store zone_check_value in a string array?
Next
case "Sheet 2"
For Each dr As DataRow In dt.Rows
Dim check_value as Boolean = array_of_string.Contains(dr(0).ToString)
'but when i got in sheet 2 the array_of_string is null
Next
Next

Answer 1

The easiest way is to use a List(Of String).
For Each dt As DataTable In xls.Tables
Dim array_of_string as List(Of String) = New List(Of String) 'i want to put the value in here
For Each dr As DataRow In dt.Rows
Dim zone_destination As String = dr(2).ToString
Dim affected_date As String = dr(7).ToString
Dim zone_check_value = zone_destination & affected_date
''''''How can i store zone_check_value in a string array?
array_of_string.Add(zone_check_value)
Next
''' Now if you really need it in array form you can cast it via:
''' Dim values() As String = array_of_string.ToArray()
Next
You might even consider:
For Each dt As DataTable In xls.Tables
Dim values As List(Of String) = New List(Of String)
dt.Rows.ForEach( Sub(item) values.Add(item(2).ToString & item(7).ToString) )
''' Now do something with values.
Next
Either way, make sure you always use the string concatenation operator & to concatenate strings. The arithmetic addition operator + will cause you problems from time to time if you use it on strings.