array key search in php

<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>

$arr = array(
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "seventeen" => 17
);
function find($mot){
  
  global $arr; // this is global variable
  $ok=false;
 foreach ($arr as $k => $v) 
    {
      if($k==$mot){
        return $v; $ok=true; // or return true;
      }
    }
  if(ok==false){ return -1; }  // or return false;
}

//call function
echo find("two");