Cannot store array values into $sum - php

Question

i made this student class
<?php
Class Student
{
private $name;
private $amountOfGrades;
private $grades=array();
function __construct(string $name,int $amountOfGrades){
$this->name=$name;
$this->amountOfGrades=$amountOfGrades;
}
function setGrades(...$grade)
{
for($i=0;$i<$this->amountOfGrades;$i++)
$this->grades[$i]=$grade;
}
function getGrades(){
return $this->grades;
}
function getAvg(){
$sum=0;
for($i=0;$i<count($this->grades);$i++)
$sum+=$this->grades[$i];
return $sum/$amountOfGrades;
}
}
?>
and this is where i test it
<?php
require_once "studentClass.php";
$Jack = new Student("Jack",3);
$Jack->setGrades(100,50,69);
print_r($Jack->getAvg());
?>
the problem is that i keep getting this error
Fatal error: Uncaught TypeError: Unsupported operand types: array + null in D:\xamp\htdocs\studentClass.php:27 Stack trace: #0 D:\xamp\htdocs\testStudent.php(6): Student->getAvg() #1 {main} thrown in D:\xamp\htdocs\studentClass.php on line 27
how am i supposed to store the amount into sum to return the avg if i cant use +=
thanks in advance

Answer 1

Your setGrades was the problem, you passed the whole grade array to every single element. Also you have to use $this->amountOfGrades not $amountOfGrades. Take a look ;)
<?php
Class Student
{
private $name;
private $amountOfGrades;
private $grades=array();
function __construct(string $name,int $amountOfGrades){
$this->name=$name;
$this->amountOfGrades=$amountOfGrades;
}
function setGrades(...$grade)
{
for($i=0;$i<$this->amountOfGrades;$i++)
$this->grades[$i]=$grade[$i];
}
function getGrades(){
return $this->grades;
}
function getAvg(){
$sum=0;
for($i=0;$i<count($this->grades);$i++) {
$sum+=$this->grades[$i];
}
return $sum / $this->amountOfGrades;
}
}
$Jack = new Student("Jack",3);
$Jack->setGrades(100,50,69);
print_r($Jack->getAvg());
?>