COMP 1000: Think Like a Computer: The PreTeXt Interactive Edition

The examples you have seen so far in this chapter show iteration over small data: strings and lists that are hard-coded into the program. In the next chapter, you are going to learn how to read from files. Reading from files gives a programmer access to much larger data sets that can be iterated over. In addition to reading from static files, there are also ways to read from live data streams, such as wind sensor data from a weather station or all the Twitter posts with a given hashtag. With the ability to iterate, programmers have the ability to make computers do massive amounts of computation and this enables things that were not really possible before because it takes people much longer to do things than computers.

One of the early ways iteration was used became powerful was for ‘mail merge’. This allowed a computer to take a list of names and addresses, and print out letters addressed to everyone on the list. This meant that a company could send letters to huge lists of people (such as to every address in a city’s phonebook), something that would have been nearly impossible for an administrative clerk to do prior to computers being standard office equipment. The introduction of iteration by computer changed things. Iteration and mail merge made it possible for people to reach a wider audience by mailing out letters. You can think of this as the original email spam! Like any tool, iteration can be used for good (sending out information about a blood donation clinic) or evil (spreading disinformation about a political candidate).