Imports System.Text.RegularExpressions
Public Class Form1
    Dim diff1 As String = ""
    Dim diff2 As String = ""
    Dim output As System.IO.StreamWriter
    Dim result As String = Environment.GetFolderPath(Environment.SpecialFolder.Desktop) + "\" + "Compared Strings.txt"
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        OpenFileDialog1.Filter = " | *.txt"
        If OpenFileDialog1.ShowDialog = DialogResult.OK Then
            TextBox1.Text = My.Computer.FileSystem.ReadAllText(OpenFileDialog1.FileName)
        End If

    End Sub
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        OpenFileDialog2.Filter = " | *.txt"
        If OpenFileDialog2.ShowDialog = DialogResult.OK Then
            TextBox2.Text = My.Computer.FileSystem.ReadAllText(OpenFileDialog2.FileName)
        End If
    End Sub

    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click

        Dim txt1(TextBox1.Text.Split(" ").Length) As String

        Dim txt2(TextBox2.Text.Split(" ").Length) As String

        txt1 = TextBox1.Text.Split(" ")

        txt2 = TextBox2.Text.Split(" ")


        For Each diff As String In txt2

            If Array.IndexOf(txt1, diff.ToString) = -1 Then
                diff2 += diff.ToString() & "<======DIFFERENT STRING"
            End If
            TextBox3.Text = diff2.ToString()

        Next
        test()

        filecrt()
    End Sub

    Private Sub test()
        Dim lines As New List(Of String)
        lines = TextBox3.Lines.ToList
        Dim FilterText = "<==="
        For i As Integer = lines.Count - 1 To 0 Step -1
            If Not Regex.IsMatch(lines(i), FilterText) Then
                lines.RemoveAt(i)
            End If
        Next
        TextBox3.Lines = lines.ToArray
    End Sub
    Private Sub filecrt()
        My.Computer.FileSystem.WriteAllText(result, TextBox3.Text, False)
    End Sub
End Class