# Calculating the exclusive or of "202005"
# V= X’32’ .XOR. X’30’ .XOR. X’32’ .XOR. X’30’ .XOR. X’30’ .XOR. X’35’ = X’05’

my $command = '202005';
print "$command length=" . length($command) . "\n";
my $result = substr($command,0,1);
for (my $i=1; $i<length($command); $i++) {
    my $c = substr($command,$i,1);
    print "$i) " . sprintf("%02X ", ord($result)) . " xor ". sprintf("%02X ", ord($c));
    $result = $result ^ $c;
    print " gives " . sprintf("%02X ", ord($result)) . "\n";
}
print sprintf("%02X ", ord($result))  . "\n";
if ( $result == "\x05" ) { print ":-)\n"; } else { print ":-(\n"; } 
print "====\n";

# THIS IS WHERE THE PROBLEM BEGINS:

# Divide by X’10:
# Y = INT ( X’05’ / X’10’ ) = X’00’

my $dividend = $result;
my $divisor = "\x10";
my $result2;
#$result2 = int($dividend/$divisor);
#print sprintf("%02X ", ord($result2))  . "\n";
# results in Illegal division by zero at kk.pl line 22.

# and this results in character zero, not NUL:
$result2 = int(ord($dividend)/ord($divisor));
print sprintf("%02X ", ord($result2))  . "\n";