Public Class Form1
    Public dblID() As Double
    Public dblQt() As Double
    Public dblPq() As Double
    Public dblDc() As Double
    Public dblTT() As Double
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        ListBox1.Items.Clear()
        ListBox1.Items.Add("ID" & vbTab & "Quantity" & vbTab & "Price/Q" & vbTab & "Discount" & vbTab & "Total")
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Dialog.ShowDialog()
    End Sub

    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        Dim sum As Double = 0.0
        For i As Integer = dblTT(0) To dblTT.Count - 1
            sum = sum + dblTT(i)
        Next
        Label1.Text = sum
    End Sub

    Private Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
        Dim txtfile As System.IO.StreamWriter
        txtfile = New IO.StreamWriter("C:\test\test.txt", False)
        For i = 0 To ListBox1.Items.Count - 1
            txtfile.WriteLine(ListBox1.Items.Item(i))
        Next
        txtfile.WriteLine("____________________________")
        txtfile.WriteLine("Total: " & "RM" & Label1.Text)
        txtfile.Close()

    End Sub
End Class