0----
1----
2----
...
17----
18----
19----

##</code><code>##

#!perl
use 5.012; # strict, //
use warnings;

my $a = 0;
while($a < 20) {
    mySubroutine();
    print "----\n";
}

sub mySubroutine {
    print $a++;
    # implied "return" from subroutine; you could make it explicit on this line if you really wanted to
}

exit;