A Queue Simulation

Let’s apply your improved understanding of classes to a programming problem. The Bank of Heather wants to open an automatic teller machine (ATM) in the Food Heap supermarket. The Food Heap management is concerned about lines at the ATM interfering with traffic flow in the market and may want to impose a limit on the number of people allowed to line up at the ATM. The Bank of Heather people want estimates of how long customers will have to wait in line. Your task is to prepare a program that simulates the situation so that management can see what the effect of the ATM might be.

A rather natural way of representing the problem is to use a queue of customers. A queue is an abstract data type (ADT) that holds an ordered sequence of items. New items are added to the rear of the queue, and items can be removed from the front. A queue is a bit like a stack, except that a stack has additions and removals at the same end. This makes a stack a LIFO (last in, first out) structure, whereas the queue is a FIFO (first in, first out) structure. Conceptually, a queue is like a line at a checkout stand or an ATM, so it’s ideally suited to the task. So one part of the project is to define a Queue class. (In Chapter 16, you’ll read about the Standard Template Library queue class, but you’ll learn more by developing your own than by just reading about such a class.)