use strict;
use warnings;
use 5.010;

use Date::Manip;
use Date::Manip::Date;

my $date1 = Date::Manip::Date->new;
my $date2 = Date::Manip::Date->new;

my $format = "%Y--%m--%d";

my $error1 = $date1->parse_format($format, "2010--03--30");
my $error2 = $date2->parse_format($format, "2010--03--31");

say $error1;  
say $error2;  

if ($error1 == 0 and $error2 == 0) { #then successfully parsed dates
    my $flag = Date_Cmp($date1, $date2);
    say $flag;
}


--output:--
0
0
Use of uninitialized value $flag in say at 1perl.pl line 21.