use vars qw($InputText);
$InputText = "";
...
my $input = $mw->Entry (-textvariable => \$InputText)->form;
...
# my $guess = int ($input->get);
my $guess = int( $InputText );
$InputText = ""; # empty it

##</code><code>##

my $input = $mw->EntryCheck(
  -textvariable => \$InputText,
  -pattern      => qr~\d~,
)->form;