<form>
  <select>
    <option value="v1">Kraków</option>
    <option value="v2">Poznań</option>
    <option value="v3">Szczecin</option>
  </select> <br>
  <input type="password" />
</form>

$suma = 0;
for ($x = 10; $x <= 20; $x++) {
    $suma += $x;
}

Kod 1.
$suma = 0;
while ($x <= 20) {
    $suma += $x;
    $x++;
}

Kod 2.
$suma = 0;
$x = 10;
while ($x <= 20) {
    $suma += $x;
    $x++;
}

Kod 3.
$suma = 0;
$x = 1;
while ($x <= 10) {
    $suma += $x;
    $x++;
}

Kod 4.
$suma = 0;
$x = 10;
while ($x <= 20) {
    $suma = $x;
    $x++;
}