random_password.php

<?php
/**
 * Quick-and-dirty password generator, fully-commented edition ;)
 *
 * Author: Abraham Vegh <[email protected]>
 */

// Our password generator, with a default length of eight
function random_password ($length = 8)
{
	// Create three ranges of characters, merge the resulting arrays into a 
	// single array, and then implode the array to form a 62-character string
	$select = implode('', array_merge(range('a', 'z'), range('A', 'Z'), range(0, 9)));
	// Calculate the length of our generated string (62, but we shouldn't have to hard-code this
	// so we can easily change the available character set later) and subtract one
	$size = strlen($select) - 1;
	// Prepare our return variable
	$return = '';

	// The divider between sections in a for() statement is a ; (semicolon) not a , (comma)
	// We start $i at 0 since arrays in PHP are zero-based
	// We finish the loop once $i is no longer less than $length, which for the default is 8 characters
	for ($i = 0; $i < $length; $i++)
	{
		// This is a fun one :)
		// Here the special { } (curly brace) symbols are used to indicate to PHP that 
		// we want to select a specific character within a string. This is similar to 
		// using [ ] (square brackets) to indicate to PHP which value in an array you 
		// want to select. We then call mt_rand() to generate a random number between zero
		// and the length of our character selection, minus 1 (remember, zero-based arrays)
		// Finally, the result of the mt_rand() call is passed directly to the $select{} and
		// the randomly selected character is added to the return variable, using the convenient
		// concatenation assignment operator, .=
		$return .= $select{mt_rand(0, $size)};
	}

	// The loop is completed, and we return (not echo - let the calling code decide what to do with it)
	return $return;
}

// Alternatively, here's a heavily compressed and optimized version of the same code :D
function rp($a=8){for($b=0,$c='',$d=implode('',array_merge(range('a','z'),range('A','Z'),range(0,9))),$e=strlen($d)-1;$b<$a;$c.=$d{mt_rand(0,$e)},$b++);return $c;}

That has got to be one of the most heavily commented snippets of code I have ever seen!

It was originally a tutorial for a beginning PHP developer friend of mine; now it's just some fun. ;)