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

my $groupCode;
my @members;

while (defined(my $line = <DATA>) || $groupCode) {
    if (defined($line) && $line !~ /^(\d+)$/) {
        chomp $line;
        push @members, $line if defined $groupCode;
        next;
    }

    if (defined $groupCode) {
        @members = '-- no members --' if !@members;
        print "$groupCode ", join(', ', @members), "\n";
    }

    $groupCode = $1;
    @members   = ();
}


__DATA__
50000
Craig
Mark
50001
Craig
Steve
50002
Durlene
Floyd
Jeremy
Kent
Leroy
Jessie
Rocky
Sean
Craig
Jeffrey
Rick