use strict;
use warnings;

my %ho = ( 
    '/*' => sub { ++$_[0] },
    '*/' => sub { --$_[0] },
);

while ( my $line = <DATA> ) { 
    my $c; 
    for ( $line =~ /(\/\*|\*\/)/g ) { 
        $c = $ho{$_}($c);
        warn "error in line $.! closing comment that isnt open\n" if $c < 0;
    }   
    warn "error in line $.! open comment isnt closed\n" if $c; 
}

__END__
korrekte zeile /* Dies ist ein Test */
define variable abc as character. /* Dies ist ein Test /* */
CODE /* KOMMENTAR /* KOMMENTAR2 */
KOMMENTAR */ CODE /* KOMMENTAR2