[Courses] [Perl] Part 2: Scalar Variables

[Karine Delvare]

Hello Dan, thanks for the Perl course!

Below is my homework, please tell me if I'm sending this too early.

> 5) Exercises
> 
> a) Write a program called 'average.pl' to calculate the average of
> the following numbers: 23, 28, 31, 17, 1

#!/usr/bin/perl -w

use strict;

my $num1 = 23;
my $num2 = 28;
my $num3 = 31;
my $num4 = 17;
my $num5 = 1;

my $total = $num1 + $num2 + $num3 + $num4 + $num5;

my $average = $total / 5;

print "Average: $average\n";

> b) Consider the following program:
> 
>    #!/usr/bin/perl -w
>    use strict;
> 
>    my $foo = 'Suzy' x 4;
>    print "$foo\n";
> 
> What does the "x" operator do? Why can't we write "4 x 'Suzy'" as
> well as "'Suzy' x 4"?

Considering that the program output was SuzySuzySuzySuzy, the "x" operator seems to concatenate a string with itself, as many times as asked for (don't know if there is a proper english term for that, but that operator is cool!)

I tried to think a bit about 4 x 'Suzy'. Perl has to know which is the string and which is the "multiplicator". In that example it could guess it, but what about 4 x 3? 4 x 3 outputs "444", but 3 x 4 outputs "3333". So operands need to be ordered.

> c) Consider the following program:
> 
>    #!/usr/bin/perl -w
>    use strict;
> 
>    my $a = q/This is string A/;   # using slash
>    my $b = q!This is string B!;   # using exclamation point
>    my $c = q:This is string C:;   # using colon
>    print "$a\n$b\n$c\n";
> 
> What does the "q" operator do? What is the advantage of using it
> rather than a single quote?

Another cool operator! The output was:
This is string A
This is string B
This is string C
So it allows to replace the quote delimiters with any character. It can be an advantage if the string to quote containes quotes and/or double-quotes (makes me think about the way you can change the regular expressions delimiters, but I'm pretty sure we will encounter these later!)

Karine