Copy Row When Cell In Column Has Value Greater Than 0

I'm creating a POS system for my wife's business. The workbook has three sheets.

On the first sheet are all the articles that her shop sells.
On A1 to D1 is the following text:

Quantity Discription Price Totalprice

B1 to D1 is already filled in. When a customer buys something, a employee only has to fill in A1, how many of what item the customer buys.

So it is possible that only 5 items have a number filled in, in A1.

Now, i have a vba, which has to search all the items which have filled in quantity and then copy row A to D to a sheet called Receipt. (Later I want to print this receipt)

Now this vba work when all the filled in cells are above each other. When there is a gap between the cells, it only copies the first row.

Here is the VBA:

Sub test()
Dim r As Range, c As Range
With Worksheets("Kassa")
Set r = Range(.Range("A1"), .Range("A1").End(xlDown))
For Each c In r
If WorksheetFunction.IsNumber(c) Then
Range(.Cells(c.Row, "A"), .Cells(c.Row, "D")).Copy

[Code] ........

When I change the second A1 in the fourth line to A200. I works, but is extremely slow. It's almost like if Excel is responding anymore. Also, when no quantities are filled in, it's also slow.