<html><body>
 <?php
  if(isSet($andmed)){
    if(ereg("^[0-9]+$", $andmed)){
      echo "Andmed sobivad";
    } else {
      echo "Andmed ei sobi";
    }
  } 
 ?><p>
 <form>
   Arv:  <input type="text" name="andmed">
 </form>
 </p>
</body></html>