[Admiral]

For Each очень удобен когда на перёд не известно количество элементов, а While и Repeat не охота пристраивать, пример. Указанный Find/FindNext/FindPrevious будут работать при табличном представлении строчки, например как в Excel при указание Range.
Сдесь же можно переделать, добавив на форму ещё RichTextBox1 (для хранения строки и отображения результата) и TextBox1(для указания чего искать), указанный код к такому виду.

Код:

Public Class Form1
    Dim FindingString As String = "asdgfsdfgsdfgsdfgStringsdfgsdfgsdfgStringsdfgsdfgsdfgString"
    Dim FindString As String = "String"
    'Dim FirstTemp As String = ""
    'Dim SecondTemp As String = ""
    'Dim ValidateTemp As Integer = 0
    Dim start As Integer = 0
    Dim indexOfSearchText As Integer = 0
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        RichTextBox1.Text = FindingString
        TextBox1.Text = FindString
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'If ValidateTemp = 0 Then
        'ValidateTemp = 1
        'FirstTemp = FindingString
        'SecondTemp = Mid(FirstTemp, InStr(FirstTemp, FindString))
        'FirstTemp = SecondTemp
        'MsgBox(FirstTemp)
        'Else
        'SecondTemp = Mid(FirstTemp, InStr(FirstTemp, FindString) + Len(FindString))
        'FirstTemp = SecondTemp
        'SecondTemp = Mid(FirstTemp, InStr(FirstTemp, FindString))
        'FirstTemp = SecondTemp
        'MsgBox(FirstTemp)
        'End If
        Dim startindex As Integer = 0

        If TextBox1.Text.Length > 0 Then
            startindex = FindMyText(TextBox1.Text.Trim(), start, RichTextBox1.Text.Length)
        End If

        ' If string was found in the RichTextBox, highlight it
        If startindex >= 0 Then
            ' Set the highlight color as red
            RichTextBox1.SelectionColor = Color.Red
            ' Find the end index. End Index = number of characters in textbox
            Dim endindex As Integer = TextBox1.Text.Length
            ' Highlight the search string
            RichTextBox1.Select(startindex, endindex)
            ' mark the start position after the position of 
            ' last search string
            start = startindex + endindex
        End If


    End Sub
    Public Function FindMyText(ByVal txtToSearch As String, ByVal searchStart As Integer, ByVal searchEnd As Integer) As Integer
        ' Unselect the previously searched string

        If searchStart > 0 AndAlso searchEnd > 0 AndAlso indexOfSearchText >= 0 Then
            TextBox1.Undo()
        End If

        ' Set the return value to -1 by default.
        Dim retVal As Integer = -1

        ' A valid starting index should be specified.
        ' if indexOfSearchText = -1, the end of search
        If searchStart >= 0 AndAlso indexOfSearchText >= 0 Then
            ' A valid ending index 
            If searchEnd > searchStart OrElse searchEnd = -1 Then
                ' Find the position of search string in RichTextBox
                indexOfSearchText = RichTextBox1.Find(txtToSearch, searchStart, searchEnd, RichTextBoxFinds.None)
                ' Determine whether the text was found in richTextBox1.
                If indexOfSearchText <> -1 Then
                    ' Return the index to the specified search text.
                    retVal = indexOfSearchText
                End If
            End If
        End If
        Return retVal
    End Function

    Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        start = 0
        indexOfSearchText = 0
    End Sub

End Class

После трёх нажатий в предыдущей версии коде выскакивает ошибка.

mrcnn,
Это всё выключается здесь Project -> Options-> Text Editor Basic -> VB Specific