Combine random letters and numbers

Question

Does any of you know how to add random letters aswel as random numbers. thanks for you help.

<?php 
session_start(); 
$image = imagecreate(, ); 
$bgcolor = imagecolorallocate($image, , ,);
$textcolor = imagecolorallocate($image, , , ); 
$code = rand(00, 99); 




$_SESSION['code'] = ($code);
imagestring($image, , , , $code, $textcolor); 
header ("Content-type: image/png"); 
imagepng($image);
?>

Answer 1

i have a function for it

function createRandomString() {
    $chars = "abcdefghijkmnopqrstuvwxyz023456789";
    srand((double)microtime()*1000000);
    $i = 0;
    $randomstring = '' ;

    while ($i <= 7) {
        $num = rand() % 33;
        $tmp = substr($chars, $num, 1);
        $randomstring = $randomstring . $tmp;
        $i++;
    }

    return $randomstring;

}

echo createRandomString();