<?php
$arraystring = ['cat','test', 'meow'];
$letter = "mow";
checkEarraystring($arraystring,$letter);
function checkEarraystring ($arraystring,$letter)
{
    $string = array();
    foreach ($arraystring as $strvalue)
    {
        if (($strvalue >= $letter) === true)
        {
            if (true){
                $string[] = $strvalue;
                echo $string;
            }
        }
        else {
            echo  "eror: $letter not found";
        }
    }
    return $string;
}
var_dump(checkEarraystring($arraystring,$letter));