dynamic tr bgcolor output with php

[NYSiRacer]

How do I make the output look like this when displaying data?
See how one row is white, and one is somewhat light gray?

Thanks.

[7khat]

$shade_ar = array("#DDDDDD", "#BBBBBB");
print "<table>";

/* YOUR LOOP CONTROL */
//
//
//

$shade = !$shade;
print "<tr bgcolor=\"" . $shade_ar[$shade] . "\">";
	print "<td>";
		//cell stuff
	print "</td>";
print "</tr>";

/* YOUR LOOP CONTROL */
//
//
//

print "</table>";

[NYSiRacer]

Thank you very much, but there're 2 things I don't understand, would you care to explain?

1. What does

   $shade = !$shade;

   mean?
   From what I understand, you're setting variable shade to be unset... doesn't quite make sense...

2. How does

   $shade_ar[$shade]

   keep looping through the array?

Thank you.

[philipolson]

Please read this faqt:

http://www.faqts.com/knowledge_base/view.phtml/aid/783/fid/9

[NYSiRacer]

7khat's code looks a lot easier than the ones here... I still have no idea what & and % do...

Does anyone know where I can find a simpler tutorial on this subject? I'd really like to learn this instead of copy & paste other people's code...

Thanks

[philipolson]

That faqt links to information on % (modulus) and & (bitwise). and explains a bit on modulus. Modulus is simpler to understand, it's the remainder. So, if a remainder exists it'll be true otherwise if no remainder exists (0), it'll evaluate to false.

$bgcolor = ($i++ % 2) ? '#ffffff' : '#000000';

For example, 4 % 2 = 0 because 2 goes into 4 exactly twice. So, it'll evaluate to false. 5 % 2 = 1 because 2 goes into 5 twice but 1 is the remainder, so this evaluates to true. $i keeps incrementing. That faqt is pretty lengthy, please follow and read the links within.

[NYSiRacer]

I think I understand modulus now, thank you very much.
How does bitwise work then? Why is it always & 1?

Thanks a lot.

[7khat]

Sorry NYSiRacer for not commenting my code. I usually don't as I am usually pretty busy. I am glad you have asked though.

In the first line, I set up an array with two elements inside it.
• $shade_ar = array("#DDDDDD", "#BBBBBB");
The two elements are the html colours you are alternating. I think you already undersand that so I will move on.

The first line inside the loop is the control variable:
• $shade = !$shade;

Essentially ! means NOT. If you have a variable that is either TRUE (1) or FALSE (0) then you can put a ! in front of it to return the opposite of what it is. By default all variables are a 0 (FALSE) before you do anything with them. So on the first loop we are making $shade the opposite of what shade already is. $shade already is a 0 so on the first pass it makes $shade to be a 1.
The next time the loop goes around, it makes shade the opposite again. $shade is now a 1, therefore $shade becomes a 0 again on the second pass. On the third pass it becomes a 1 and the forth a 0. So essentially $shade just flip flops between 1 and 0 each time $shade = !$shade; is run.

In the next line we have this:
• $shade_ar[$shade]
When you access an array, you do so by asking for the array ($shade_ar) and what element inside it ([$shade]). The first element can be accessed with a 0, and the second with a 1 and so on to the end of the array.

$shade_ar[0] = #DDDDDD
$shade_ar[1] = #BBBBBB

So on the first run, this part returns '#BBBBBB' and on the second '#DDDDDD' and on the third it's back to '#BBBBBB', thus your colours are alternating. It's just a very simple method that I dreamt up when I made my forums, and it's the method I still use: http://www.almostrammstein.com/nf/forums/view_forum.html?fid=1

Feel free to use this code at will. If you find a simpler way, let me know 🙂

[NYSiRacer]

Interesting method, but I've already finished my application using modulus. One question though, it doesn't look like your code will work with more than 2 colors from what I see... right?

[sarahk]

Aaaah, well it wouldn't. It's operating on a true/false swap.

alternate way to code
$shade = !$shade;
is
$shade = 1 - $shade;

both do the same thing and may or may not be more readable.

If you need to do a greater colour loop try

//set $maxColours to be the length of your colour array.
$maxColours = 5;
// and then later on
$shade++;
if ($shade > $maxColours) $shade = 0;

[7khat]

No - it's not designed for more than two colours, but is all the scope I use for alternating colours, and that's all that was asked for in this problem.
If you wanted more colours, I'd do it his way: Which is just how sarahk put it minus the $maxColours variable.

$shade_ar = array("#AAAAAA", "#BBBBBB", "#CCCCCC", "#DDDDDD");

// LOOP

$shade++;
if ($shade >= count($shade_ar)) $shade = 0;

//TABLE STUFF with $shade_ar[$shade]
..
..
..

// END LOOP
..
..
..