I am still a newbie, but / therefore - what is wrong with using hash here (with keys as line numbers and values as bases)?

#!/usr/bin/perl -l
use strict;
use warnings;

print "If an array element is a line number and a base together as a s
+tring:";

my %positions;

for my $line (split /\n/, <<'END') 
1 ACAC
2 AGAC
3 AGTC
4 ACCA
END

{
    next if $line =~ /[GT]/;
    my ($number, $bases ) = split / /, $line;
    $positions{$number} = $bases;    
}

for my $number ( sort keys %positions )
{
    print "$number => $positions{$number}";
    print "Just print a number $number";
}

print "If there is an array element for a line number and for a base:"
+;

my @array = ( qw (1 ACAC 2 AGAC 3 AGTC 4 ACCA) );
%positions = ();
for (my $i = 0; $i < @array; $i +=2 )
{
    my ($number, $bases ) = @array[$i, $i+1];
    next if $bases =~ /[GT]/;
    $positions{$number} = $bases;
}

for my $number (sort keys %positions)
{
    print "$number => $positions{$number}";
    print "Just print a number $number";
}
[download]

It prints:

If an array element is a line number and a base together as a string:
1 => ACAC
Just print a number 1
4 => ACCA
Just print a number 4
If there is an array element for a line number and for a base:
1 => ACAC
Just print a number 1
4 => ACCA
Just print a number 4
[download]