我可以將12345678.9輸出成12,345,678.90嗎?

當然可以,PHP中有個函數number_format,函數原型:
        string number_format
        (
           float number,
           int decimals,
           string dec_point,
           string thousands_sep
        )
    舉個例子:
        <?
        $num = 12345678.9;
        echo number_format($num).'<br>'; //會4捨5入
        echo number_format($num,2).'<br>';
        echo number_format($num,2,':').'<br>'; //這種寫法是錯誤的
        echo number_format($num,2,':','-').'<br>';
        ?>
    輸出結果為:
        12,345,679
        12,345,678,90
        Warning: Wrong parameter count for number_format() in /data/homepage/test/number_format.php on line 5
        12-345-678:90