simple PHP integer conversion

Question

convert this: $300 to this : 300

• can't do it with intval() or (int) typecasting
• if the non-numerical character is suffixed (300$), both works and returns 300
• if it is prefixed it returns 0
• the non-numerical character can be anything other than the "$"(i.e. "askldjflksdjflsd")

Please help

EDIT : list items are not requirements, they are a list of activities and observations I have made. Sorry:(

Answer 1

$number = filter_var($number, FILTER_SANITIZE_NUMBER_INT);

Answer 2

preg_match('/\d+/', $num, $matches);
echo $matches[0];

Answer 3

$number = (integer) str_replace('$', '', $number);

Answer 4

You can get rid of all the non-digits in the input by doing:

$input = preg_replace('/\D/','',$input);

Answer 5

print (int) trim('$300', '$');

No need for a regex.