Question

Using PHP (other languages, using common built-ins are welcome), how can I get a random (or pseudo-random) number that does NOT match a certain criteria?

IE: I want $x = rand(0, 99) but only if ($x % 9) != 0.

What is a clean acceptable way to constrain random numbers to a criteria like that?

As an example, using a while() loop, and possibly breaking when we have something that meets our criteria, then using the random number after the loop?:

while ( ($rand_key = array_rand($array_of_items)) && ($rand_key % 9 == 0) ) 
{ 
    // Do nothing?
}

Or something like:

while ( $rand_key = array_rand($array_of_items) ) 
{ 
    if ( $rand_key % 9 == 0 ) {
        break;
    }
}

Or is there a more concise or appropriate way to accomplish this?

Answer 1

One of the rare cases where a do-while loop actually helps

$testData = array( 7, 8, 9 );

do {
  $rand = array_rand( $testData );
} while ( $testData[$rand] % 9 == 0 );

echo $testData[$rand];