}
    return false;
}
$student_id = $_GET['student_id'];
$subject_ids = $_POST['subject_ids'];
$student_grades = Grade::get_by_sql("SELECT * FROM " . T_STUDENT_GRADES . " WHERE " . C_GRADE_STUDENT_ID . "=" . $student_id);
$student_subjects = array();
foreach ($student_grades as $student_subject) {
    array_push($student_subjects, Subject::get_by_id($student_subject->subject_id));
}
$warnings = "";
foreach ($subject_ids as $id) {
    $thestudent = Student::get_by_id($student_id);
    $thestudent->semester = Subject::get_by_id($id)->semester;
    $thestudent->update();
    if (Grade::exists($id, $student_id)) {
        $newgrade = Grade::get_by_subj_stud($id, $student_id);
        $newgrade->delete();
    }
    $newgrade = new Grade();
    $newgrade->subject_id = $id;
    $newgrade->student_id = $student_id;
    $newgrade->grade = 0;
    $newgrade->create();
    $pre_subject = Subject::get_by_id($id);
    if (!EvaluatedSubject::exists($id, $student_id)) {
        $grade = Grade::get_by_subj_stud($pre_subject->id, $student_id);
        $gradepre = Grade::get_by_subj_stud($pre_subject->prereq_subject_id, $student_id);
        if (has_prerequisite($pre_subject->prereq_subject_id, $student_subjects)) {
            if ($gradepre != null) {
                if (Grade::get_by_subj_stud($pre_subject->prereq_subject_id, $student_id)->grade <= 74) {