When working with program code, very often you are designing a procedure (or “algorithm”) that solves a problem in a general way. For instance, in the previous chapter one of the exercises had you calculate the wholesale price for a stack of books, for a given book price and a given number of books. The code you wrote did not solve this problem for a general case, but only for the specific case of 60 books costing 24.95 per book. If you want to write code that solves problems in a more general way, you need to use variables that store values.