PHP错误：未定义的变量

Question

can anyone told me what is my error. i know it only notice. All is work well but only show this notice. How to fix this? :

this is the code :

if (isset($_GET['match']) && $_GET['match'] == 'one') {
    $checked_match_one = ' checked="checked"';
    $page_string .= SEP.'match=one';
} else {
    $_GET['match'] = 'all';
    $checked_match_all = ' checked="checked"';
    $page_string .= SEP.'match=all';
}

the error it tell me this :

Notice: Undefined variable: page_string in C:\xampp\htdocs\msigilearnv2\admin\enrollment_attendance.php on line 110
Done writing the list into excel. Download

Answer 1

Simple.Initialize $page_string before using it(before the if statement we can say) like

$page_string = '';
if (isset($_GET['match']) && $_GET['match'] == 'one') {
    $checked_match_one = ' checked="checked"';
    $page_string .= SEP.'match=one';
}