Can PHP tell the diff. between even and odd?

AndrewWest

I was just thinking about some possibilities (Easier alternating row colors, and a few others) if it could. Can anyone verify, either way?

AndrewWest

I was also just thinking. Is this the way.. alternating color row does it?

I was thinking of

  if (!$num % 2) {
    // Odd number
  } else {
    // Even number
  }

or is bitwise faster?

  if ($num & 1) {
    // Odd number
  } else {
    // Even number
  }

AndrewWest

Alright I'm using this

$i = $row['id'];
if ( $i&1 )
{
    $post_class = 'forumcell';
}
else
{
    $post_class = 'forumcell_odd';
}

But..it only changes the cell color for ID #2 opposed to even numbers. I'm missing the concept here I think.

tsinka

Hi,

do you want to change the color depending on the id or depending on the current row number in e.g. a HTML table while looping through a result set and printing table rows ?

Thomas

AndrewWest

I would like to do it by whether the ID is even or odd.

tsinka

Ok,

if you print out just the ids ... are there other even ids despite id #2 ?

Thomas

tsinka

I think it should be

<?PHP
if (($i&1) == 1) 
{ 
    $post_class = 'forumcell_odd'; 
} 
else 
{ 
    $post_class = 'forumcell'; 
}
?>

since &1 would return 1 if the number is odd.

AndrewWest

I have 4 rows showing, and there was no editing done to them - So yes.

167,168,169,170

tsinka

Please post the complete code including the query and the while loop.

Thomas

drawmack

The bitwise & creates an output where the bits that are set in both the input and output are set.

Here is the example detailed (using 8bit values for simplicity's sake).

for($i=0;$i<5;$i++) {
    if($i & 1) 
        echo 'here 1<br />';
    else 
        echo 'here 2<br />';
} //end for

Okay there is the code now let's take a look under the hood at what's really going on.

First pass, $i = 0
    00000000 & 00000001 = 00000000
    This is false so the else executes 
Second pass, $i = 1
    00000001 & 00000001 = 00000001
    This is true so the if executes
Third pass, $i = 2
    00000010 & 00000001 = 00000000
    This is false so the else executes
Fourth pass, $i = 3
    00000011 & 00000001 = 00000001
    This is true so the if executes
Fifth pass, $i = 4
    00000100 & 00000001 = 00000000
     This is false so the else executes

Try echoing out the ids maybe that is the problem you're running into. Or it could even be a signed vs. unsigned problem.