CHAPTER 4
Control Flow
A common metaphor given to beginning programmers is following a recipe. That
metaphor can be useful, but it has an unfortunate weakness: to achieve repeatable
results in the kitchen, one has to minimize choices. Once a recipe is refined, the idea
is that it is followed, step by step, with little to no variation. Occasionally, of course,
there will be choices: “substitute butter for lard,” or “season to taste,” but a recipe is
primarily a list of steps to be followed in order.
This chapter is all about change and choice: giving your program the ability to
respond to changing conditions and intelligently automate repetitive tasks.
If you already have programming experience, especially in a lan‐
guage with a syntax inherited from C (C++, Java, C#), and are
comfortable with control flow statements, you can safely skim or
skip the first part of this chapter. If you do, however, you won’t
learn anything about the gambling habits of 19th-century sailors.
A Control Flow Primer
Chances are, you’ve been exposed to the concept of a flowchart, which is a visual way
of representing control flow. As our running example in this chapter, we’re going to
write a simulation. Specifically, we are going to simulate a Midshipman in the Royal
Navy in the mid-19th century playing Crown and Anchor, a betting game popular at
the time.
The game is simple: there’s a mat with six squares with symbols for “Crown,”
“Anchor,” “Heart,” “Club,” “Spade,” and “Diamond.” The sailor places any number of
55
