#!/usr/bin/perl -w

use strict;
use Data::Dumper;

my %student;

open STUDENT, "<student.txt" or die "Cannot open student.txt: $!\n";
while (<STUDENT>) {
    my @student = split(':');
    $student{$student[0]} = { name => $student[1] };
}
close STUDENT;

open GRADES, "<grades.txt" or die "Cannot open grades.txt: $!\n";
while (<GRADES>) {
    my @grades = split(' ');
    $student{$grades[0]}->{grade}->{$grades[1]} = $grades[2];
}
close GRADES;

print Dumper(\%student);
print "\n------------------------------\n";

foreach my $id (sort keys %student) {
    print "Id: $id - $student{$id}->{name}\n";

    my $graderef = $student{$id}->{grade};
    foreach my $exam (sort keys %$graderef) {
        print "  Exam: $exam grade: $graderef->{$exam}\n";
    }
}