To sum it up when you buy something in the shop youll want to change the currency attribute to currency-however much the item costs. Also youll only want to be able to do that if currency is equal to or greater then the amount the item costs so you cant buy it if you dont have enough. That will be a condition in your touch is pressed rule on the item or whatever other rule you have to trigger the buy. Then change the attribute that contains that item to attribute+1 so it adds one of the item to the inventory.
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To sum it up when you buy something in the shop youll want to change the currency attribute to currency-however much the item costs. Also youll only want to be able to do that if currency is equal to or greater then the amount the item costs so you cant buy it if you dont have enough. That will be a condition in your touch is pressed rule on the item or whatever other rule you have to trigger the buy. Then change the attribute that contains that item to attribute+1 so it adds one of the item to the inventory.