echo validatePIN("1234")."\n";
echo validatePIN("12345")."\n";
echo validatePIN("123456")."\n"; 
echo validatePIN("")."\n";

function validatePIN($pin){
	$len=strlen($pin);
	if (strlen($pin)!=4 && strlen($pin)!=6){
		return "PIN is invalid";
	}
	for ($i=0; $i<$len; $i++)
	$ASCII=ord($pin[$i]);
	if (!(47<$ASCII && $ASCII<58)){
		return "PIN is invalid";
	}
	return "PIN is valid";
}