1. Associative arrays
We  access the element of an array by indexes. 
For the array:
@books = ("Physics", "Mathematics", "Chemistry", "H2o", "Computer Science", 1010101);
The first element of this array is $books[0]. The second element is $books[1], 
and so on. 
With Perl, we can create arrays which the elements are accessed by string. 
These arrays are called associative arrays.

Example:
-------
%books = ("Physics", "Mechanics","Mathematics", 123,"Chemistry", "H2o",
"Computer Science", 1010101);


@discipline = %books;	
for ($i=0; $i<8;++$i) {
print "$discipline[$i]\n";
}
for ($i=0; $i<8;++$i) {
print "$disciplines[$i]\n";
}


outputs:

Chemistry
H2o
Computer Science
1010101
Physics
Mechanics
Mathematics
123


Now, with the associative arrays

$books{"Physics"};
print $books{"Physics"};
$books{"Mathematics"};	
print "$books{'Mathematics'}\n";
$books{"Chemistry"};
print $books{"Chemistry"};
$books{"Computer Science"};	
print "$books{'Computer Science'}\n";


outputs:

Mechanics123
H2o1010101

That is for each key, we have its value



Now with a list array

@disciplines = %books;	

for ($i=0; $i<8;++$i) {
print "$disciplines[$i]\n";
}


ouputs:

Chemistry
H2o
Computer Science
1010101
Physics
Mechanics
Mathematics
123




foreach $book (keys %books)
{
	print "the key is $book\n";
}
foreach $book (values %books)
{
	print "the value is $book\n";
}



ouputs:

the key is Chemistry
the key is Computer Science
the key is Physics
the key is Mathematics
the value is H2o
the value is 1010101
the value is Mechanics
the value is 123



2. Arrays related functions:

2.1. scalar
To get how many elements are in an array, use scalar
my @books = ("Physics","Mathematics","Chemistry", "Geography");
my $elements = scalar(@books);
will return 
4


2.2. shift(@array)
To remove one element from the beginning, we use the 
"shift ()" function
Example:
my @letters = qw ( a b c d );
shift(@letters);
will give: b c d

2.3. unshift( @array, LIST)
To add elements to the BEGINNING of an array.
Example:
my @letters = qw ( a b c d );
unshift(@letters, 'x');
will give: x a b c d 

2.4. sort(@array)

The function sort() sorts an array alphabetically
my @digits = ( 45, 56, 12, 3, 235, 567 );
my @sorted_digits = sort(@digits);
print @sorted_digits;
will sort them by considering them as characters.

Use instead:
my @digits = ( 45, 56, 12, 3, 235, 567 );
my @sorted_digits = sort {$a<=>$b} (@digits);
print @sorted_digits;

will sort the array .

2.5. reverse(@array)

The reverse() function returns an array in reverse order.


2.6. splice(@array)

We use splice() to add or remove elements into or out 
of an array. The syntax is:
splice ( ARRAY , OFFSET , LENGTH , LIST );

my @digits = ( 45, 56, 12, 3, 235, 567 );
splice(@digits, 1, 0, '777');
warn join(" ", @digits);

outputs:
45 777 56 12 3 235 567 at C:\www\PERL\test.pl line 4.