This appendix contains the answers to the excerses that appear throughout the book.

## Answers to Chapter 2 Exercises

1. Here’s one way to do it:

```#!/usr/bin/perl -w
\$pi = 3.141592654;
\$circ = 2 * \$pi * 12.5;
print "The circumference of a circle of radius 12.5 is \$circ.\n";```

As you see, we started this program with a typical `#!` line; your path to Perl may vary. We also turned on warnings.

The first real line of code sets the value of `\$pi` to our value of π. There are several reasons a good programmer will prefer to use a constant[1] value like this: it takes time to type `3.141592654` into your program if you ever need it more than once. It may be a mathematical bug if you accidentally used `3.141592654` in one place and `3.14159` in another. There’s only one line to check on to make sure you didn’t accidentally type `3.141952654` and send your space probe to the wrong planet. It’s easier to type `\$pi` than π, especially if you don’t have Unicode. And it will be easy to maintain the program in case the value of π ever changes.[2]

Next we calculate the circumference, storing it into `\$circ`, and we print it out in a nice message. The message ends with a newline character, because every line of a good program’s output should end with a newline. Without it, you might end up with output looking something like this, depending upon your shell’s prompt:

```The circumference of a circle of radius 12.5 is
78.53981635.bash-2.01\$[]```

The box represents the input cursor, blinking at the end ...

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