Вызов функции

function auth($sql,$connect,$row,$query) {
 //Тут код
}

function App($sql,$connect,$row,$query){
//Тут надо обратиться к функции auth
}

function auth($sql,$connect,$row,$query) {
 $a="$sql,$connect,$row,$query";
 return ($a);
}
 
function App($sql,$connect,$row,$query){
$b=auth ($sql,$connect,$row,$query);
return ($b);
}
 
$c=App(1,2,3,4);
echo "$c"

 Fatal error: Call to undefined function auth()

class m {
 
function auth($sql,$connect,$row,$query) {
 $a="$sql,$connect,$row,$query";
 return ($a);
}
 
function App($sql,$connect,$row,$query){
$b=$this->auth($sql,$connect,$row,$query);
return ($b);
}
}
 
$m1=new m;
$c=$m1->App(1,2,3,4);
echo $c;

 Catchable fatal error: Object of class mysqli could not be converted to string in W:\domains\local.helpdesk.ru\sql\query.php on line 201

function unionTables ($sql,$connect,$row,$query) {
        $sql = "SELECT a.id_eq,a.id_br,a.id_user,b.br,e.eq,u.user FROM `application` a LEFT OUTER JOIN `equipment` e ON a.id_eq=e.id_eq LEFT OUTER JOIN `breaking` b ON a.id_br=b.id_br LEFT OUTER JOIN `users` u ON a.id_user=u.id_user";
        $query = mysqli_query($connect,$sql) or die("ERROR: ".mysqli_error());
        while($row = mysqli_fetch_array($query)) {
            echo '<table><tr><td>'.$row['eq'].'</td><td>'.$row['br'].'</td><td>'.$row['user'].'</td></tr></table>';
        }
        $a = "$sql,$connect,$row,$query";
        return ($a);
    }
     function auth($sql,$connect,$row,$query) {
    #ERROR_REPORTING(~E_ALL);
    $login = htmlspecialchars(trim(stripslashes($_POST['login'])));
    $password = htmlspecialchars(trim(stripslashes($_POST['password'])));
    if(isset($_POST['login']) && ($_POST['password'])) {
        $sql = "SELECT `login`,`password` FROM `auth` WHERE `login` = '$login' AND `password` = $password";
        $query = mysqli_query($connect,$sql);
        $row = mysqli_fetch_array($query);
            if($password == $row['password'] && $login == $row['login']) {
                echo "<script>alert('Добро пожаловать,$login')</script>";
                     if($login == 'Abramov') {
                        $b = $this->unionTables($sql,$connect,$row,$query);
                    }
                    elseif($login == 'Naumov') {
                        
                    } 
                }
            else {
                echo "<script>alert('Не правильно введены данные')</script>";
            }
        }
        return ($b);
 }

function unionTables ($connect) {
        $sql = "SELECT a.id_eq,a.id_br,a.id_user,b.br,e.eq,u.user FROM `application` a LEFT OUTER JOIN `equipment` e ON a.id_eq=e.id_eq LEFT OUTER JOIN `breaking` b ON a.id_br=b.id_br LEFT OUTER JOIN `users` u ON a.id_user=u.id_user";
        $query = mysqli_query($connect,$sql) or die("ERROR: ".mysqli_error());
        while($row = mysqli_fetch_array($query)) {
            echo '<table><tr><td>'.$row['eq'].'</td><td>'.$row['br'].'</td><td>'.$row['user'].'</td></tr></table>';
        }
        return ($query);
    }
     function auth($connect) {
    #ERROR_REPORTING(~E_ALL);
    $login = htmlspecialchars(trim(stripslashes($_POST['login'])));
    $password = htmlspecialchars(trim(stripslashes($_POST['password'])));
    if(isset($_POST['login']) && ($_POST['password'])) {
        $sql = "SELECT `login`,`password` FROM `auth` WHERE `login` = '$login' AND `password` = $password";
        $query = mysqli_query($connect,$sql);
        $row = mysqli_fetch_array($query);
            if($password == $row['password'] && $login == $row['login']) {
                echo "<script>alert('Добро пожаловать,$login')</script>";
                     if($login == 'Abramov') {
                        $b = $this->unionTables($connect);
                    }
                    elseif($login == 'Naumov') {
                        
                    } 
                }
            else {
                echo "<script>alert('Не правильно введены данные')</script>";
            }
        }
        return ($b);
 }