function getTheHighestDigit($n) {
$max = 0;
while ($n != 0) {
if ($n % 10 > $max) $max = $n % 10;
$n = (int)($n / 10);
}
return $max;
}
$n = 213;
echo getTheHighestDigit($n) . "\n";
$n = 76594;
echo getTheHighestDigit($n) . "\n";
$n = 76852;
echo getTheHighestDigit($n);
/*
run:
3
9
8