Invoice Generator using checkboxes - Undefined Offset [2] PHP Codeigniter - php

Question

I am trying to generate multiple invoices in a school management system.
Here is the issue:
For example I have 10 students in the DB
I am able to generate the invoices if the students are selected in consecutive order.
Student 1, Student 2, Student 3, Student 4
But once I miss a student from the consecutive order and try to generate in a random order it gives me an undefined offset error:
Student 1, Student 4, Student 5, Student 7
Here is the code:
for($x = 1; $x <= count($this->input->post('studentId')); $x++) {
$insert_data = array(
'class_id' => $this->input->post('className'),
'section_id' => $this->input->post('sectionName'),
'student_id' => $this->input->post('studentId')[$x],
'payment_name_id' => $payment_name_id
);
$status = $this->db->insert('payment', $insert_data);
}
return ($status === true ? true : false);
The same also applies to editing the invoices once it has been generated.
I even tried changing the for loop to a while loop for that one, which does not give me any error but it just doesn't save if the students selected are in a random order:
$x = 1;
$form_fields = count($this->input->post('editStudentId'));
while($x <= $form_fields) {
if(!empty($this->input->post('editStudentId')[$x])) {
$update_payment_data = array(
'class_id' => $this->input->post('editClassName'),
'section_id' => $this->input->post('editSectionName'),
'student_id' => $this->input->post('editStudentId')[$x],
'payment_name_id' => $id
);
$status = $this->db->insert('payment', $update_payment_data);
}
$x++;
}
return ($status === true ? true : false);
IMAGE - SELECTING STUDENTS:
IMAGE- POST SAVE WITH JUST 2 out of the 4 I SELECTED:

Answer 1

Replace for with foreach:
foreach ($this->input->post('studentId') as $studentId) {
$insert_data = array(
'class_id' => $this->input->post('className'),
'section_id' => $this->input->post('sectionName'),
'student_id' => $studentId,
'payment_name_id' => $payment_name_id
);
$status = $this->db->insert('payment', $insert_data);
}