Visual Basic.NET - Comparar dos cadenas de caracteres

me.textbox1.text="abcdefg"

me.textbox2.textr="acf"

Dim v_long as integer = me.textbox1.text.trim.lenght

dim v_letra as string

For x=1 to v_long

     If me.textbox2.contains(v_letra=mid(x,1))

     else

        me.textbox3.text=v_letra=mid(x,1)

    End if

Next

resultado:

me.textbox3.text

Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click

	Me.versionoriginal.Text = "abcdefg"

	Me.cambiosrealizados.Text = "acf"

	Dim v_cambios As String = Me.cambiosrealizados.Text.Trim

	Dim v_long As Integer = Me.versionoriginal.Text.Trim.Length

	Dim v_letra As String = ""

	For x = 1 To v_long

		v_letra = Mid(Me.versionoriginal.Text, x, 1)

		If v_cambios.Contains(v_letra) = True Then

		Else

			'este es un label

			Me.comentariocambios.Text = Me.comentariocambios.Text + v_letra

		End If

	Next

End Sub