版上有程式高手嗎!!

請問,有程式高手可以幫忙解釋下面的程式碼每一行各是什麼意思嗎??
我只略懂大概...感激不盡...

Dim a As Integer
a = 0
If chb1.Checked Then
a += a + lbl4.Text * txtbox1.Text
lbloutput.Text &= "高麗菜" & vbTab & txtbox1.Text & "份" & vbNewLine
End If
If chb2.Checked Then
a += a + lbl5.Text * txtbox2.Text
lbloutput.Text &= "豆乾" & vbTab & txtbox2.Text & "份" & vbNewLine
End If
If chb3.Checked Then
a += a + lbl6.Text * txtbox3.Text
lbloutput.Text &= "海帶" & vbTab & txtbox3.Text & "份" & vbNewLine
End If
If chb4.Checked Then
a += a + lbl7.Text * txtbox4.Text
lbloutput.Text &= "肉乾" & vbTab & txtbox4.Text & "份" & vbNewLine
End If
lbloutput.ForeColor = Color.Red
lbloutput.Font = New Font("細明體", 18, FontStyle.Bold)
lbloutput.Text &= "總金額" & vbTab & a & "元" & vbNewLine
lbloutput.Text &= "****************************" & vbNewLine
If a >= 1000 Then
txt1000.Text += a \ 1000
txt500.Text += (a - txt1000.Text * 1000) \ 500
txt100.Text += (a - txt1000.Text * 1000 - txt500.Text * 500) \ 100
txt50.Text += (a - txt1000.Text * 1000 - txt500.Text * 500 - txt100.Text * 100) \ 50
txt10.Text += (a - txt1000.Text * 1000 - txt500.Text * 500 - txt100.Text * 100 - txt50.Text * 50) \ 10
txt5.Text += (a - txt1000.Text * 1000 - txt500.Text * 500 - txt100.Text * 100 - txt50.Text * 50 - txt10.Text * 10) \ 5
txt1.Text += (a - txt1000.Text * 1000 - txt500.Text * 500 - txt100.Text * 100 - txt50.Text * 50 - txt10.Text * 10 - txt5.Text * 5) / 1