How do I change for toy,boy,etc?

[Yelu]

<?php
    echo "Enter the number of nouns you like to change its plural: ";
    $f = fopen("php://stdin","r");
    $num = rtrim(fgets($f));
    $input = array($num);
    function Change_Plural($noun)
    {
        switch (true)
        {
            case (substr($noun,-1) == 's'):
            case (substr($noun,-2) == 'sh'):
            case (substr($noun,-2) == 'ch'):
            case (substr($noun,-1) == 'o'):
            case (substr($noun,-1) == 'x'):
                 echo $noun.'es'."\r\n";
                 break;
            case (substr($noun,-1) == 'f'):
                 echo substr_replace($noun,'ves',-1)."\r\n";
                 break;
            case (substr($noun,-2) == 'fe'):
                 echo substr_replace($noun,'ves',-2)."\r\n";
                 break;
            case (substr($noun,-1) == 'y'):
                                           {
                                               switch(true)
                                               {
                                                   case (substr($noun,-2) != 'ay'):
                                                case (substr($noun,-2) != 'ey'):
                                                case (substr($noun,-2) != 'iy'):
                                                case (substr($noun,-2) != 'oy'):
                                                case (substr($noun,-2) != 'uy'):
                                                     echo substr_replace($noun,'ies',-1)."\r\n";
                                                     break;
                                                default:
                                                        echo $noun.'s'."\r\n";
                                            }
                                           }
                                           break;
            default:
                    echo $noun.'s'."\r\n";
        }
    }
    for ($j = 0; $j < $num; $j++)
    {
        $input[$j] = rtrim(fgets($f));
    }
    echo "\r\n";
    for ($j = 0; $j < $num; $j++)
    {
        Change_Plural($input[$j]);
    }