#!/usr/bin/env perl
use strict; use warnings;

my %classroom = (
    10 => {
        classroomName    => 'classroom1',
        student          => {
            9534   => {
                studentName    => 'John',
                studentSurname => 'Doe',
                age            => '12',
            }
        },
    },
);

my $room = 10; my $kid = 9534;
print <<END;
Student $kid in room $classroom{$room}{classroomName} is 
$classroom{$room}{student}{$kid}{studentName} $classroom{$room}{student}{$kid}{studentSurname},
who is age $classroom{$room}{student}{$kid}{age}.


END

# Add a classroom
$classroom{11} = { 
    classroomName => 'classroom2',
};

# Add a student to new classroom
$classroom{11}{student}{5489} = {
    studentName    => 'Mary',
    studentSurname => 'Smith',
    age            => 13,
};

# Add a student to old classroom
$classroom{10}{student}{3456} = {
    studentName    => 'Jim',
    studentSurname => 'Baker',
    age            => 14,
};

# Print structure
print "Students listed by classroom\n";
for my $cid (keys %classroom) {
    print "Classroom ID $cid, name $classroom{$cid}{classroomName}\n";
    for my $sid (keys %{$classroom{$cid}{student}}) {
        my $student = $classroom{$cid}{student}{$sid}; #for less typing
        print '   ', join ' ', $sid,
            @{$student}{qw/studentName studentSurname age/};
        print "\n";
    }
}

# Print raw structure
use Data::Dumper;
print "\n\n", Dumper %classroom;