how to make a underline in richtextbox in vb 2005

Hi all,

Can anybody can help with my problem.

i have two richtextbox that compare if the wring word is inputted..
i want just to underline the words that the user have type wrong..
my problem is the next word that is wrong or not equal i not underline but the first word is being underline.

Code:

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        Dim Str1 As Array
        Dim str2 As Array
        On Error Resume Next
        Str1 = Split(Trim(richtextbox1.text), " ")
        str2 = Split(Trim(richtextbox2.text), " ")

        For i As Integer = 0 To Str1.Length - 1
       
            If String.Compare(Str1(i).ToString, str2(i).ToString, False) <> 0 Then
           
                If Str1(i).ToString <> str2(i).ToString Then
          'underline the data that a wrong word
          'the equal string is the error that needs to be underline
          'the problem occurs on the wrong word
                displayerrorstrring=str2(i).ToString
               
                End If

                errorcounter = errorcounter + 1
            End If

        Next

PS.. it must be done on lostfocus event.

Really appropriated your help. i'am really lost here.
Thanks.

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You might try asking in a VB.Net forum instead of here in General Developer.