Generate random number 1-10 upon registration without repeat

Question

I have an event with 10 spaces available for booking. When a user registers for the event, I need to assign them a random draw number from 1 through 10. I will include this number in the confirmation email they receive after registration.

I know I can generate the number like this:

$num = random_int(1, 10); 

But I can't figure out how to ensure that the number assignment is unique. I can't give someone a number that has already been assigned to another registrant. People will not register at the same time, so I somehow need the function to check against all the previously assigned numbers before assigning a random number from the remaining numbers.

If it matters, event registrants will only be logged-in users, so I could assign something to their user meta if needed.

How would you go about this? Thank you!

Answer 1

All right, I figured it out. But if someone wants to suggest something better, please feel free and I will mark it correct.

// array of previously-assigned numbers (get this by looping through the registered users -not shown)
$numbers_already_taken = array(3,8,1);

// get all the numbers between 1-10
$numbers = range(1, 10);

// shuffle the numbers so they are in random order
shuffle($numbers);

// set up variable to hold this user's draw #
$draw = '';
    
// loop through the available numbers
foreach ($numbers as $number) {
    
    // ignore numbers that have already been assigned
    if (!in_array($number, $numbers_already_taken)) {

      // assign the first matching draw number (break stops it)
      $draw = $number;
      break;

    }
   
}

echo 'Your Draw Number: ' . $draw;

// save $draw to the user's profile or booking (not shown)