<select name="number">

<option value="number">test</option></select>

<?php

echo "<select name='number'>";

for ($i = 100; $i <= 999; $i++) {

    echo "<option value='$i'>$i</option>";

}

echo "</select>";

 

 

echo "<select name='number'>";

$i = 100;

while ($i <= 999) {

    echo "<option value='$i'>$i</option>";

$i++;

}

echo "</select>";

?>