Function of php: after the value is processed by function, then spit back the function display, how to do it?

hypothetical

function number($id){
   //....

 sizeof($array); // 
}
<?= number(id);?>

when number is complete, there will be a value
how can I write
to my function so that it will be printed ?

return number (); ?

Mar.05,2021

return $array;

return sizeof ($array);

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