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Imports System.Net
Imports System.IO
Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim WC As New WebClient 
        Dim HtmlText As String, Result As String
        HtmlText = WC.DownloadString(New Uri("http://site.ru")) 
        WC.Dispose()
        Result = Pars(HtmlText, ("<title>"), ("</title>")) 
        MsgBox(Result)
    End Sub
    Public Function Pars(ByRef strSource As String, ByRef strStart As String, ByRef strEnd As String) As String
        Dim iPos As Integer, iEnd As Integer
        Dim strResult As String
        iPos = strSource.IndexOf(strStart, 0)
        iEnd = strSource.IndexOf(strEnd, iPos + strStart.Length)
        If iPos <> -1 AndAlso iEnd <> -1 Then
            strResult = strSource.Substring(iPos + strStart.Length, iEnd - (iPos + strStart.Length))
        End If
        Return strResult
    End Function

Public Function Pars1(ByRef strSource As String, ByRef strStart As String, ByRef strEnd As String, Optional ByRef startPos As Integer = 0) As String
        Dim iPos As Integer, iEnd As Integer, lenStart As Integer = strStart.Length
        Dim strResult As String
        strResult = String.Empty
        iPos = strSource.IndexOf(strStart, startPos)
        iEnd = strSource.IndexOf(strEnd, iPos + lenStart)
        If iPos <> -1 AndAlso iEnd <> -1 Then
            strResult = strSource.Substring(iPos + lenStart, iEnd - (iPos + lenStart))
        End If
        Return strResult
    End Function

Module Module1
 
    Sub Main()
        Dim Text As String = "Маша ела кашу, ла ла ла"
        Console.WriteLine(CountMatches(Text, "ла"))
        Console.Read()
    End Sub
    'Функция поиска количества совпадений в строке определенной подстроки
    'один из недостатков-ошибка по количеству совпадений из-за извлечения подстрок из строки
    'для поиска совпадений целых слов не пригодна
    Private Function CountMatches(ByVal StringToSearch As String, ByVal SerchFor As String) As Integer
        Dim Position As Integer = 0
        Dim Matches As Integer = 0
        Do
            Position = StringToSearch.IndexOf(SerchFor, Position)
            If Position <> -1 Then
                Matches += 1
                Position += SerchFor.Length
            End If
        Loop Until Position = -1
        Return Matches
    End Function
End Module

 Private Sub Button1_Click(sender As Object, e As System.EventArgs) Handles Button1.Click
        Dim Client As New System.Net.WebClient
        Dim Str As String
        Str = Client.DownloadString(New Uri("http://www.yandex.ru"))
        Dim Reader = New SgmlReader
        Reader.InputStream = New System.IO.StringReader(Str)
        Dim Xmldocument = New Xml.XmlDocument(Reader.NameTable)
        Xmldocument.Load(Reader)
 
        Dim links As Xml.XmlNodeList = Xmldocument.GetElementsByTagName("a")
        TextBox1.AppendText("Найдено: " & links.Count.ToString)
    End Sub