use warnings;
use strict;   
########################
# DATABASE Input:    ###
#################################################### 
print "\n\n Please ENTER Database Name (.txt): ";
 my $DNAfilename=<STDIN>;
 chomp $DNAfilename;   
# open the file, or exit:  
 unless (open(DNAFILE, $DNAfilename) ) {
 print "Cannot open file \"$DNAfilename\"\n\n";
 exit;}    
 my @DNA= <DNAFILE>; 
print"\n $DNAfilename Database:\n\n";
print @DNA;
print"\n";
##########################
## CODE STARTS HERE:  
##########################
 {package Student;
   sub new {    
   my ($class, $name, $age, $regd_no)=@_;
        my $objref={ NAME => $name,
                     AGE => $age,
                     REGD_NO => $regd_no  
                   };   
        return bless $objref, $class;}

    sub display
    { my ($self) = @_;
      if ($self)
        { print ' Student Name:  ', $self->{NAME},      "\n";
            print ' Age (yr):    ', $self->{AGE},       "\n";
            print ' Regd no:     ', $self->{REGD_NO},   "\n";
          }
      }
   }    
my @students;  
open (DNAFILE, '<', $DNAfilename) or die "Perl says $!"; 
while (<DNAFILE>) {
  chomp; 
  push @students, Student->new(split /:/);
}    
print"\n WELCOME to Students' Database:\n"; 
print"\n Enter the Registration Number to view the details: ";
 my $reg=<STDIN>; chomp $reg; 
 my $result1=(find_student($reg)->display());
print"\n Detailed Information for Registration No. $reg:\n
 $result1\n";   

 sub find_student
  {my ($regd_no) = @_;
  print"\n\n";
  print"\n The details of the Regn No. $reg are:\n\n";
  for (@students) {
   return $_ if $_->{REGD_NO} eq $regd_no;
  }
  return undef;  
  }  
  print"\n\n";
exit;