choose random value only once

问题

My page loads a random background image every time it loads:

<?php
    $input = array(1, 2, 3, 4, 5, 6, 7, 8);
    $num = array_rand($input, 1);
    $bg = "img/bg" . $num . ".jpg";
?>

But I want it to do that only once. I want the image to remain the same after a visitor submits a form, for example, thereby reloading the page.

I've tried if($bg=NULL) etc, but to no avail - I guess $bg becomes null again every time the page reloads.

Many thanks in advance!

回答1:

You can use Session variable or cookies if is not set, you choose a background, if is set, you do nothing

回答2:

Got it (thanks to Ricardo):

<?php
    session_start();
    if (!isset($_SESSION['num'])) {
        $input = array(1, 2, 3, 4, 5, 6, 7, 8);
        $_SESSION['num'] = array_rand($input, 1);
    }

    $bg = "img/bg" . $_SESSION['num'] . ".jpg";
?>

来源：https://stackoverflow.com/questions/14429795/choose-random-value-only-once