How to convert this VB.NET code to C#.
Private Function ConvertHTMLTablesToDataSet(ByVal HTML As String) As DataSet
' Declarations
Dim ds As New DataSet
Dim dt As DataTable
Dim dr As DataRow
Dim dc As DataColumn
Dim TableExpression As String = "<table[^>]*>(.*?)</table>"
Dim HeaderExpression As String = "<th[^>]*>(.*?)</th>"
Dim RowExpression As String = "<tr[^>]*>(.*?)</tr>"
Dim ColumnExpression As String = "<td[^>]*>(.*?)</td>"
Dim HeadersExist As Boolean = False
Dim iCurrentColumn As Integer = 0
Dim iCurrentRow As Integer = 0
' Get a match for all the tables in the HTML
Dim Tables As MatchCollection = Regex.Matches(HTML, TableExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase)
' Loop through each table element
For Each Table As Match In Tables
' Reset the current row counter and the header flag
iCurrentRow = 0
HeadersExist = False
' Add a new table to the DataSet
dt = New DataTable
' Create the relevant amount of columns for this table (use the headers if they exist, otherwise use default names)
If Table.Value.Contains("<th") Then
' Set the HeadersExist flag
HeadersExist = True
' Get a match for all the rows in the table
Dim Headers As MatchCollection = Regex.Matches(Table.Value, HeaderExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase)
' Loop through each header element
For Each Header As Match In Headers
dt.Columns.Add(Header.Groups(1).ToString)
Next
Else
For iColumns As Integer = 1 To Regex.Matches(Regex.Matches(Regex.Matches(Table.Value, TableExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase).Item(0).ToString, RowExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase).Item(0).ToString, ColumnExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase).Count
dt.Columns.Add("Column " & iColumns)
Next
End If
' Get a match for all the rows in the table
Dim Rows As MatchCollection = Regex.Matches(Table.Value, RowExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase)
' Loop through each row element
For Each Row As Match In Rows
' Only loop through the row if it isn't a header row
If Not (iCurrentRow = 0 And HeadersExist = True) Then
' Create a new row and reset the current column counter
dr = dt.NewRow
iCurrentColumn = 0
' Get a match for all the columns in the row
Dim Columns As MatchCollection = Regex.Matches(Row.Value, ColumnExpression, RegexOptions.Multiline Or RegexOptions.Singleline Or RegexOptions.IgnoreCase)
' Loop through each column element
For Each Column As Match In Columns
' Add the value to the DataRow
dr(iCurrentColumn) = Column.Groups(1).ToString
' Increase the current column
iCurrentColumn += 1
Next
' Add the DataRow to the DataTable
dt.Rows.Add(dr)
End If
' Increase the current row counter
iCurrentRow += 1
Next
' Add the DataTable to the DataSet
ds.Tables.Add(dt)
Next
Return ds
End Function