Entry

How can I show rows from a database in a table with alternating colors?

How can I use the Modulus Operator in PHP?

In a search result, how do you change the table (with the results) row color every result?

May 14th, 2002 20:37
Alder Rus, Jens Clasen, Amit Arora, Philip Olson, Robert Sherman, Wedgx, Nathan Wallace,

If it's simply in a loop, this may suit your needs: 
    $bgcolor = ($i++ & 1) ? '#ffffff' : '#000000'; 
Which will alternate between the two. You should first initialize $i 
outside the loop as $i = 0; Also, look into "Modulus" as the following 
also works (a little less efficient but who's counting): 
    $bgcolor = ($i++ % 2) ? '#ffffff' : '#000000'; 
Now let's say you wanted to alternate between four colors, you could do 
something like: 
    $colors = array('black','green','blue','yellow'); 
And within the loop: 
    $bgcolor = $colors[$i++ % 4]; 
Which makes modulas more flexible then bitwise (the &) for this sort of 
thing. One thing to remember is % is the modulus operator, it tells you 
the remainder after the two numbers are divided.  I hope that makes 
sense and if not, search google ... it's not PHP specific. Here's a 
simple example: 
    $i = 0; 
    while($row = mysql_fetch_array($result)) { 
        $bgcolor = ($i++ & 1) ? '#ffffff' : '#000000'; 
        print "<tr bgcolor='$bgcolor'>\n";
        print "\t<td>". $row['name'] ."</td>\n</tr>\n"; 
    }
Spend some time on it as it'll eventually make sense.  For kicks, 
here's yet another example:
    $colors = array('black','green','blue','yellow');
    $num_colors = count($colors);
    $i = 0;
    for ($a=0; $a <= 20; $a++) {
        $bgcolor = $colors[$i++ % $num_colors];
        print "$bgcolor<br>\n";
    }
Granted we could have just used $a instead of $i but again, do as you 
wish.  If the use of ? and : looks funny to you, this is called a 
ternary conditional operator, it's briefly mentioned here:
  http://www.php.net/manual/language.expressions.php
  http://www.cs.bilkent.edu.tr/~will/courses/CS101/slides03/tsld036.htm
So essentially, the following provide identical results in PHP:
  if ($fruit == 'banana') {
    $myfav = 'my favorite fruit!';
  } else {
    $myfav = 'not a banana';
  }
  $myfav = ($fruit == 'banana') ? 'my favorite fruit!' : 'not a banana';
Th bitwise operator we used above (the &) can be read about here :
  http://www.php.net/manual/language.operators.bitwise.php
  http://lal.cs.byu.edu/cs130/Lectures/lect24.html
The modulus remainder operator (the %) can be read about here:
  http://www.php.net/manual/language.operators.php
To explain modulus, it returns the remainder.  For example:
  0 % 2   // 0                                        // false
  1 % 2   // 1                                        // true
  2 % 2   // 0 // 2 goes into 2 once, none remain     // false
  3 % 2   // 1 // 2 goes into 3 once, then 1 remains  // true
  4 % 2   // 0 // 2 goes into 4 twice, none remain    // false
When something is 0, it is considered false so the above statements 
prove false which then assigns the "false color."  Next time around 1 
is returned which evaluates to true.  The "true color" is then chosen.  
This continues on and on throughout the loop.  The number goes from 0 
to n, as we increment it (in the above example we increment $i by 1 
every time)
  if (true) {
    'do something';
  } else {
    'do something else'
  }
Now for example, to use our modulus knowledge, let's return false every 
third time, as to evalate true twice for every false:
  0 % 3   // 0 // false
  1 % 3   // 1 // true
  2 % 3   // 2 // true
  3 % 3   // 0 // false
  4 % 3   // 1 // true
  5 % 3   // 2 // true
  6 % 3   // 0 // false
  7 % 3   // 1 // true
  8 % 3   // 2 // true
  9 % 3   // 0 // false
See how that works?  0 evaluates to false, all other numbers evaluate 
as true and from that, our bidding is done.
And lastly, read about incrementing here:
  http://www.php.net/manual/language.operators.increment.php
With all this knowledge, you should be able to create all kinds of 
different alternating colored rows :-)