Make C++ program to reverse a file format

I need a simple-to-use converter/importer program that does two functions. This program should analysis the file data and allow me to Convert/Extract the data from .dat format file to .txt/xls/csv/sylk format. This program should analysis the file data and allow me to Convert/Import the data from .txt/xls/csv/sylk back to the .dat format. Two .dat files, namely item and slk, are required to be reverse to properly structured readable format. Both files are packed/compressed/compiled into this weird dat format. Item dat is a single file by itself. Slk dat is multiple files packed. Original data are number and texts only. Most likely a .sylk format originally. When open on notepad, most texts are readable but numbers are all unreadable. As for structure, I do have the algorithm for it. It is GBK encoded. Files language are mixed English and Chinese. Game mmorpg related. Image of the .dat files : [login to view URL] I uploaded 1 of the dat file. Please have a check on the dat that I have uploaded before consider bidding.