This appendix contains the answers to the exercises that appear throughout the book.
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 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
one place and
3.14159 in another.
There’s only one line to check on to make sure you didn’t
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. 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 of ...