Generate Random Numbers with given length in PHP

For doing this use the following code in PHP development.

function gen_random($length=32)
{
$final_rand='';
for($i=0;$i< $length;$i++)
{
$final_rand .= rand(0,9);

}

return $final_rand;
}
echo gen_random(10)."<br/>";//random number with length 10
echo gen_random()."<br/>";//random number with length 32