Why does this PHP function call work only once?

Question

I've wrote a simple array, and I would use it to print an html list option set, with a selected element. My problem starts if I try to print multiple lists in my page, because only the first list is printed correctly, why?

<?php


$units = array (
'0' => 'Units',
'kJ' => 'Kilojoule: kJ',
'g' => 'Grams: g',
'mg' => 'Milligrams: mg',
'mcg' => 'Micrograms: mcg, µg');

function unit_select_option ($attributes, $code = "") {
    global $units;
    $html = "<select title=\"Kilojoule: kJ;&#13;Grammi: g;&#13;Milligrammi: mg;&#13;Microgrammi: mcg, µg;\" $attributes>\r";

    while (list($key, $name) = each($units)) {
        if ($key == "0") {
            $html .= "  <option title=\"$name\" value='$key'>$name</option>\r";
        } else if ($key == $code) {
            $html .= "  <option title=\"$name\" selected=\"selected\" value='$key'>$key</option>\r"; 
        } else {
            $html .= "  <option title=\"$name\" value='$key'>$key</option>\r";
        }
    }
    $html.= "</select>\r";
    return $html;
}

print unit_select_option ('class="units_select"', "g");
print unit_select_option ('class="units_select"', "mg");
print unit_select_option ('class="units_select"', "mcg");
?>

the code shouldn't be nothing strange but I haven't found the issue because the page doesn't return any error.

html code:
<select title="Kilojoule: kJ;&#13;Grammi: g;&#13;Milligrammi: mg;&#13;Microgrammi: mcg, µg;" class="units_select">
    <option title="Unit&agrave;" value='0'>Unit&agrave;</option>
    <option title="Kilojoule: kJ" value='kJ'>kJ</option>
    <option title="Grammi: g" selected="selected" value='g'>g</option>
    <option title="Milligrammi: mg" value='mg'>mg</option>
    <option title="Microgrammi: mcg, µg" value='mcg'>mcg</option>
</select>
<select title="Kilojoule: kJ;&#13;Grammi: g;&#13;Milligrammi: mg;&#13;Microgrammi: mcg, µg;" class="units_select">
</select>
<select title="Kilojoule: kJ;&#13;Grammi: g;&#13;Milligrammi: mg;&#13;Microgrammi: mcg, µg;" class="units_select">
</select>

Answer 1

each() advances the internal array cursor. Because $units is a global variable, your first call of unit_select_option() advances the cursor to the end of $units, and there it remains for the subsequent calls.

You need to rewind your array using reset($units); at the end of unit_select_option().

PHP Documentation: reset

Answer 2

You should reset the array pointer: use reset()

But why don't you use a foreach loop?

foreach($units as $key => $name){ ... }

And don't use global, it's evil. Declare $units array as static within the function body.