To be honest, Sergey is probably right - doing this kind of thing in a batch file is not the easiest way: it's a bit like trying to move house using a Ford Ka. You can do it...but it's going to take some serious effort and you'd be much better off using a Transit instead. :laugh:
But, if you must...
The SET statement normally works with string values, but you can force it to integers by using the "/A" option:
SET /A money=1000
Then, you can do things like:
SET /A money=money-100
But seriously? It's going to be difficult, time consuming and a general PITA to maintain - you would be much better off investing your time in learning a "proper" programming language - even QuickBasic would be easier (and if you only knew how much I dislike basic in all it's varieties, you would know how unlikely I am to use that phrase).
I would suggest trying in C# - it's pretty easy to pick up, and it really will make your task a whole lot easier...