@Override
    public char getGrade() {
        char grade;
        if (score >= 80) {
            grade = 'A';
        } else if (score >= 70) {
            grade = 'B';
        } else if (score >= 60) {
            grade = 'C';
        } else if (score >= 50) {
            grade = 'D';
        } else {
            grade = 'F';
        }
        return grade;
    }