Another use for random numbers is choosing from banner ads. Suppose you've signed up three sponsors for your Web site. Each has a single banner you promise to display on an equal proportion of hits to your site. To accomplish this, generate a random number and match each number to a particular banner. It is used a switch statement on a call to mt_rand. In a situation like this, you don't need to worry too much about using good seeds. You simply want a reasonable distribution of the three choices. Someone guessing which banner will display at midnight poses no security risk.

Generating a Session Identifier

<?
//Seed the generator
mt_srand(doubleval(microtime()) * 100000000);
//choose banner
switch(mt_rand(1,3))
{
case 1:
$bannerURL =$bannerImage = "leon.jpg";
break;
case 2:
$bannerImage = "php_lang.jpg"; break; default:$bannerImage = "phptr.jpg";
}
//display banner
print("<A HREF="$bannerURL">"); print("<IMG SRC= "$bannerImage" ");
print("WIDTH="400" HEIGHT="148" BORDER="0"
>");
print("</A>");
?>