Beginner"s Introduction to Perl 5.10 exercise solution commentary

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I just finished working on a solution for the exercises provided in the
tutorial located here:

A Beginner's Introduction to Perl 5.10 - Perl.com
http://bit.ly/dHvsqC
(shortened to prevent cutoff)

Instructions for the exercise:
"Given a month and the day of the week that's the first of that month,
print a calendar for the month."

and would like to request feedback on the solution with regards to ways
I could potentially improve this code. Also any mention of perldocs or
other documentation to look over would be most appreciated. Thank you
ahead of time for any feedback.

Note: Leap year logic is intentionally left out to make sure I
understood the basics.

===3D Code ===3D
use warnings;
use strict;

use List::Util qw(first);

my %days_in_months =3D (
'Jan' =3D> 31,
'Feb' =3D> 29,
'Mar' =3D> 31,
'Apr' =3D> 30,
'May' =3D> 31,
'Jun' =3D> 30,
'Jul' =3D> 31,
'Aug' =3D> 31,
'Sep' =3D> 30,
'Nov' =3D> 31,
'Dec' =3D> 31
);

my @days_of_the_week =3D ('Sun','Mon', 'Tue', 'Wed', 'Thu', 'Fri','Sat');=


sub PrintHeaders {
print "Sun\tMon\tTue\tWed\tThu\tFri\tSat\n";
}

sub GetDayOfWeekIndex {
my $day_of_the_week_name =3D shift;
my $index_value =3D first { $days_of_the_week[$_] eq
$day_of_the_week_name } 0 .. $#days_of_the_week;
return $index_value;
}

sub PrintCalendar {
my($month, $start_day) =3D @_;
my $start_day_of_the_week =3D GetDayOfWeekIndex $start_day;
my $day_of_week_counter =3D 0;

# If the first day of the week doesn't start on Sunday
# we will need to add some visual padding.
if($start_day_of_the_week !=3D $day_of_week_counter)
{
# -1 is used here because we need to loop this for
# the days up to but not including the start day of
# the week
for my $i (0..($start_day_of_the_week-1))
{
print "\t";
}

$day_of_week_counter =3D $start_day_of_the_week;
}

for my $day (1..$days_in_months{$month})
{
print $day;

if($day_of_week_counter == $#days_of_the_week)
{
print "\n";
$day_of_week_counter =3D 0;
}
else
{
print "\t";
$day_of_week_counter++;
}
} ## end for

}

PrintHeaders;
PrintCalendar "Jan", "Fri";

== Output ==
Sun Mon Tue Wed Thu Fri Sat
1 2
3 4 5 6 7 8 9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30
31=09

(Verified by looking at a calendar for January 2010 with Friday as the
first day of the week.)
--=20
Onteria
Will you change the world, or will the world change you?


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Re: Beginner"s Introduction to Perl 5.10 exercise solution commentary

On Sun, Dec 12, 2010 at 7:52 PM, Onteria wrote:
> I just finished working on a solution for the exercises provided in the
> tutorial located here:
>
> A Beginner's Introduction to Perl 5.10 - Perl.com
> http://bit.ly/dHvsqC
> (shortened to prevent cutoff)
>
> Instructions for the exercise:
> "Given a month and the day of the week that's the first of that month,
> print a calendar for the month."
>
> and would like to request feedback on the solution with regards to ways
> I could potentially improve this code. Also any mention of perldocs or
> other documentation to look over would be most appreciated. Thank you
> ahead of time for any feedback.
>

wow, that's a bunch of code. this is why i use Date::Manip; for this
sort of thing. it includes leap year. however, if you want to add leap
year to this, maybe use something like if ($year % 4)... don't
remember when leap year is, so adjust as needed. i also store all of
my timestamps in epoch format which makes things easy (print time() ).

however, if this is just an exercise and nothing practical, ignore all
of this. however, since Date::Manip is pretty mature, you might look
through that code for some decent ideas.

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Re: Beginner"s Introduction to Perl 5.10 exercise solution commentary

Hi Onteria,

On Monday 13 December 2010 02:52:42 Onteria wrote:
> I just finished working on a solution for the exercises provided in the
> tutorial located here:
>
> A Beginner's Introduction to Perl 5.10 - Perl.com
> http://bit.ly/dHvsqC
> (shortened to prevent cutoff)
>
> Instructions for the exercise:
> "Given a month and the day of the week that's the first of that month,
> print a calendar for the month."
>
> and would like to request feedback on the solution with regards to ways
> I could potentially improve this code. Also any mention of perldocs or
> other documentation to look over would be most appreciated. Thank you
> ahead of time for any feedback.
>
> Note: Leap year logic is intentionally left out to make sure I
> understood the basics.

OK.

>
> === Code ===
> use warnings;
> use strict;
>

Nice.

> use List::Util qw(first);
>
> my %days_in_months = (
> 'Jan' => 31,
> 'Feb' => 29,
> 'Mar' => 31,
> 'Apr' => 30,
> 'May' => 31,
> 'Jun' => 30,
> 'Jul' => 31,
> 'Aug' => 31,
> 'Sep' => 30,
> 'Nov' => 31,
> 'Dec' => 31
> );

1. You should not be using one-space indentation, because the code is
difficult to read that way. Either use tabs or use something like four spaces.

>
> my @days_of_the_week = ('Sun','Mon', 'Tue', 'Wed', 'Thu', 'Fri','Sat');

You can use qw() here:

my @days_of_the_week = qw(Sun Mon Tue Wed Thu Fri Sat);

See:

* http://perlmeme.org/howtos/perlfunc/qw_function.html

* http://perldoc.perl.org/functions/qw.html

>
> sub PrintHeaders {
> print "Sun\tMon\tTue\tWed\tThu\tFri\tSat\n";
> }

This can be written using (untested):

print join("\t", @days_of_the_week), "\n";

And you can also use say in perl 5.10 and above.

Furthermore, I see you're using CamelCase for functions. You should be using
words_separated_by_underscore for that too.

>
> sub GetDayOfWeekIndex {
> my $day_of_the_week_name = shift;
> my $index_value = first { $days_of_the_week[$_] eq
> $day_of_the_week_name } 0 .. $#days_of_the_week;
> return $index_value;
> }

Maybe use a hash here instead. And the variables are too long and redundant
for my taste.

>
> sub PrintCalendar {
> my($month, $start_day) = @_;

You should have a space between the "my" and the "(".

> my $start_day_of_the_week = GetDayOfWeekIndex $start_day;
> my $day_of_week_counter = 0;
>
> # If the first day of the week doesn't start on Sunday
> # we will need to add some visual padding.
> if($start_day_of_the_week != $day_of_week_counter)
> {
> # -1 is used here because we need to loop this for
> # the days up to but not including the start day of
> # the week
> for my $i (0..($start_day_of_the_week-1))
> {
> print "\t";
> }

This can be done without a loop using the "x" operator":

http://perldoc.perl.org/perlop.html#Multiplicative-Operators

>
> $day_of_week_counter = $start_day_of_the_week;
> }
>
> for my $day (1..$days_in_months{$month})
> {
> print $day;
>
> if($day_of_week_counter == $#days_of_the_week)
> {

It will be less confusing if you increment $day_of_week_counter before the
conditional and check that it equals to @days_of_the_week in scalar context.

> print "\n";
> $day_of_week_counter = 0;
> }
> else
> {
> print "\t";
> $day_of_week_counter++;
> }
> } ## end for
>
> }
>
> PrintHeaders;
> PrintCalendar "Jan", "Fri";
>

You should also make sure you print a trailing newline because otherwise some
shells won't display the last line properly.

Regards,

Shlomi Fish

> == Output ==
> Sun Mon Tue Wed Thu Fri Sat
> 1 2
> 3 4 5 6 7 8 9
> 10 11 12 13 14 15 16
> 17 18 19 20 21 22 23
> 24 25 26 27 28 29 30
> 31
>
> (Verified by looking at a calendar for January 2010 with Friday as the
> first day of the week.)

--
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What Makes Software Apps High Quality - http://shlom.in/sw-quality

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Re: Beginner"s Introduction to Perl 5.10 exercise solution commentary

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Hi Shlomi,

Thanks for your detailed response, I really appreciate it. It looks as
though I need to tweak my editor a bit more and do more research on perl
style guidelines. I'll also take a look at the documentation you
provided to expand my knowledge more. Once again thanks for taking the
time to answer!

Best Regards,
Onteria
--=20
Onteria
Will you change the world, or will the world change you?


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