input： allow single data input, using standard input device, i.e., keyboard, or batch data in plain text file format
output: monitor
a warehouse, has some initial repository, this initial data is stored in a plain text file, load this file at beginning of program, must serialized/deserialized
Then, everyday, there would be some incoming goods or some outgoing goods, label as positive data and negative data
these data can be input via keyboard or datafile as descrbed above.
Calculating result should be output to a text file and serialized, store in your local harddisk.
Every time when program starts, load the data file, deserializes it and stores in a list or whatever you think is appropriate.
Goal: To create a fixed format report, display every item's outgoing quantity, incoming quantity and the lastest repository base on the data stored in serialized file.