use strict;

my @ss = ('SSD','PERS','SS','CHILD SUP');
my %checked = map {$_ => 1} ('SSD','PERS');

foreach my $ss (@ss) {
   print qq|<input type="checkbox" name="ss" value="$ss"|,
      $checked{$ss} ? ' selected' : '', ">\n"
   ;
}

##</code><code>##

my %checked = map {$_ => 1} split(/,/,$INPUT{'ss'})