#!usr/bin/perl
use Tk;
use strict;
use warnings;
#
my $value;
my $mw=new MainWindow;
my $ent = $mw -> Entry(-textvariable=> \$value,
	-validate=>'key',
	-validatecommand=>sub { $_[0] =~ /-{0,1}\d+$/ },
	-invalidcommand=> \&lam_num_error)->pack();
my $print_button = $mw->Button(-text=>"Print",
    -command=> \&print, -font=>"ansi 10 bold")->pack();
#
my $reset_frm = $mw -> Frame();
$reset_frm->pack(-fill=>'both');
my $reset_button = $reset_frm->Button(-text=>"Reset",
    -command=> \&do_reset, -font=>"ansi 10 bold")->pack();
MainLoop;
sub print {
	print "$value";
}
sub do_reset {
	$ent->delete(0,'end');
}
sub lam_num_error {
    $mw->messageBox(-message=>"The input must be an integer.");
}