LuisEn,
As Mike Ellis said, for the Rockwell Software (Allen-Bradley PLC's), there are two separate functions CTU (Count Up) and CTD (Count Down). To use those in the Parking Lot program, it would be necessary to add rungs to make each counter have the same Accumulated Value. I have done this in similar programs and it is no big deal.
But for the Automation DIrect PLC's there are CNT (Count) and UDC (Up/Down Counter). The CNT only counts UP 0 to 9999, but the UDC will count up and/or down from 0 to 99,999,999. It has three ladder rung inputs: Up, Down, and Reset, and also a Preset value that ranges from 0 to 99,999,999. When it reaches the Preset Value, the UDC Counter bit is set and stays set until the UDC Reset input goes on. There is no DONE or COUNT bit equivalent to the Rockwell DN and CNT bits.