如何阻止我的IF语句冲突，如何选择优先级？

Question

I'm quite new to PHP and I've been asked to write a script that displays an image based on time. I've deducted that I need to use PHP's native 'date' function for this and up until I was asked to implement bank holidays and Christmas into it, all went well.

I tried to add the Christmas and bank holidays in as a separate if statement but that was when disaster struck and I haven't been able to figure out why it's come to a halt. I've tried using an online PHP validator to no avail.

Please don't be afraid to throw details and jargon at me as I really wish to expand my knowledge of PHP and rely less on the support of web forums in the future!

Here is the code:

<?php

        // Date-time (day of month, month) 

        $d = date('j'); // Day of month: Numeric without leading zeroes
        $m = date('n'); // Month: As above
        $D = date('w'); // Day of week
        $H = date('G'); // Hour of day

        // REGULAR OPENING TIMES
        // Closed before 9am on weekdays
        if ($H < 9 && $D <= 5) :
                $showroom_img = '/media/gbu0/pagehead/showroom_closed.jpg';
        // Open before 5pm (but after 9, as first if statement overrides this) on weekdays
        elseif ($H < 17 && $D <= 5) :
                $showroom_img = = '/media/gbu0/pagehead/showroom_open.jpg';
        // Closed before 10am on Saturdays
        elseif ($H < 10 && $D == 6) :
                $showroom_img = = '/media/gbu0/pagehead/showroom_closed.jpg';
        // Open between 10am and 2pm on Saturdays
        elseif ($H < 14 && $H > 10 && $D == 6) :
                $showroom_img = = '/media/gbu0/pagehead/showroom_open.jpg';
        // Any other time, display closed image :)
        else :
                $showroom_img = = '/media/gbu0/pagehead/showroom_closed.jpg';
        endif;

        // Holidays 2014

        $xmas_starts = ($d == 23 && $m == 12 && $d > 17);
        $xmas_ends   = ($d == 26 && $m == 12);
        $nyd         = ($d == 1 && $m = 1);

        // Easter Friday: April 18
        // Easter Monday: April 21
        // Early Spring B/H: May 5
        // Late Spring B/H: May 26
        // Summer B/H: August 25

        // All bank holidays: 10am - 2pm

        if( date >= $xmas_starts && $day <= $xmas_ends ) :
                $xmas = true;
        elseif( date = $nyd ) :
                $nyd = true;
        else :
                $bankhol = false;
        endif;

        if( $xmas = true ) :
                $showroom_img = "/media/gbu0/pagehead/showroom_xmas.jpg";
        elseif( $bankhol = true && date('F', 'j') = strpos('April 18' || 'April 21' || 'May 5' || 'May 26' || 'August 25') || date('w') = 6 ) :
                $showroom_img = "/media/gbu0/pagehead/showroom_bhol.jpg";
        elseif( date('w') = 7 ) :
                $showroom_img = "/media/gbu0/pagehead/showroom_closed.jpg";
        else :
                $showroom_img = "/media/gbu0/pagehead/showroom_open.jpg";
        endif;

?>

Answer 1

First of all. I noticed a couple of bugs :

elseif( date = $nyd ) :
                $nyd = true;

and

if( $xmas = true ) :
                $showroom_img = "/media/gbu0/pagehead/showroom_xmas.jpg";

In PHP, '=' is the assignment operator, used to assign value to a variable. What you need here is the comparison operator, '=='. For example :

if( $xmas == true ) :

Or you could also do (it's pointed out in a comment already) :

if( $xmas ) :

Rgarding priority, the if statements are going to be checked in the order you write them in your code. TO ensure that a condition gets the highest priority, that has to be checked first.