php中函数内使用static修饰变量

function num(){
    $a = 0;
    echo $a;
    $a++;
}
num();num();num();
//输出000

function num(){
    static $a = 0;
    echo $a;
    $a++;
}
num();num();num();
//输出012

function getcolor() {
    static $colorvalue;
    if($colorvalue == ‘#FFF‘)
        $colorvalue = ‘#000‘;
    else
        $colorvalue = ‘#FFF‘;
    return $colorvalue;
}
echo "<table border=1>";
for ($i=0;$i<10;$i++) {
    $bgcolor = getcolor();
    echo "<tr bgcolor=$bgcolor>";
    echo "<td>$i</td>";
    echo "</tr>";
}