Generating a random numbers and letters

This is a more extensive method that I use constantly to generate random numbers, letters or mixed:

function assign_rand_value($num) {

    // accepts 1 - 36
    switch($num) {
        case "1"  : $rand_value = "a"; break;
        case "2"  : $rand_value = "b"; break;
        case "3"  : $rand_value = "c"; break;
        case "4"  : $rand_value = "d"; break;
        case "5"  : $rand_value = "e"; break;
        case "6"  : $rand_value = "f"; break;
        case "7"  : $rand_value = "g"; break;
        case "8"  : $rand_value = "h"; break;
        case "9"  : $rand_value = "i"; break;
        case "10" : $rand_value = "j"; break;
        case "11" : $rand_value = "k"; break;
        case "12" : $rand_value = "l"; break;
        case "13" : $rand_value = "m"; break;
        case "14" : $rand_value = "n"; break;
        case "15" : $rand_value = "o"; break;
        case "16" : $rand_value = "p"; break;
        case "17" : $rand_value = "q"; break;
        case "18" : $rand_value = "r"; break;
        case "19" : $rand_value = "s"; break;
        case "20" : $rand_value = "t"; break;
        case "21" : $rand_value = "u"; break;
        case "22" : $rand_value = "v"; break;
        case "23" : $rand_value = "w"; break;
        case "24" : $rand_value = "x"; break;
        case "25" : $rand_value = "y"; break;
        case "26" : $rand_value = "z"; break;
        case "27" : $rand_value = "0"; break;
        case "28" : $rand_value = "1"; break;
        case "29" : $rand_value = "2"; break;
        case "30" : $rand_value = "3"; break;
        case "31" : $rand_value = "4"; break;
        case "32" : $rand_value = "5"; break;
        case "33" : $rand_value = "6"; break;
        case "34" : $rand_value = "7"; break;
        case "35" : $rand_value = "8"; break;
        case "36" : $rand_value = "9"; break;
    }
    return $rand_value;
}

function get_rand_alphanumeric($length) {
    if ($length>0) {
        $rand_id="";
        for ($i=1; $i<=$length; $i++) {
            mt_srand((double)microtime() * 1000000);
            $num = mt_rand(1,36);
            $rand_id .= assign_rand_value($num);
        }
    }
    return $rand_id;
}

function get_rand_numbers($length) {
    if ($length>0) {
        $rand_id="";
        for($i=1; $i<=$length; $i++) {
            mt_srand((double)microtime() * 1000000);
            $num = mt_rand(27,36);
            $rand_id .= assign_rand_value($num);
        }
    }
    return $rand_id;
}

function get_rand_letters($length) {
    if ($length>0) {
        $rand_id="";
        for($i=1; $i<=$length; $i++) {
            mt_srand((double)microtime() * 1000000);
            $num = mt_rand(1,26);
            $rand_id .= assign_rand_value($num);
        }
    }
    return $rand_id;
}

---

USAGE:

Basically I have a main function with the array, then I call secondary functions to build my string based on the length parameter:

Letters:

$str = get_rand_letters(8); // Only Letters

Numbers:

$str = get_rand_numbers(8); // Only Numbers

AlphaNumeric:

$str = get_rand_alphanumeric(8); // Numbers and Letters

This Question is answered by Kerrek SB, but this may help someone searching for a more extensive and flexible way.

Use uniqid

$desired_length = 10; //or whatever length you want
$unique = uniqid();

$your_random_word = substr($unique, 0, $desired_length);

Step 1: Create an alphabet, $alph = "0123456789abcde...";.

Step 2: Create a random number, $n = rand(0, ALPHSIZE-1);, or use mt_rand().

Step 3: Get the appropriate index in the alphabet: $alph[n];

Rinse and repeat steps 2 and 3 for as many times as you need characters.

If you want strong statistical properties (like uniformness), you should work a little harder with the random number, but this should get you started. (I think the statistical properties of that should be sufficient.)

---

OK, might as well spell it out:

$alph = "012...";
function make_random_string($N)
{
  $s = "";
  for ($i = 0; $i != $N; ++$i)
    s .= $alph[mt_rand(0, ALPHSIZE - 1)];
  return $s;
}

And here's the version that takes a custom alphabet:

function make_random_custom_string($N, $alphabet)
{
  $s = "";
  for ($i = 0; $i != $N; ++$i)
    s .= $alphabet[mt_rand(0, strlen($alphabet) - 1)];
  return $s;
}

Example: 10 random odd digits: make_random_custom_string(10, "13579");

<?php
echo substr(sha1(mt_rand()),17,6); //To Generate Random Numbers with Letters.
?>