def add_grade():
    subject = input("Enter Subject: ").strip()
    marks = int(input("Enter Marks (0-100): "))

    cur.execute(
        "INSERT INTO grades (roll_no, subject, marks) VALUES (?, ?, ?)",
        (roll_no, subject, marks)
    )

def view_report_card():
    cur.execute("SELECT subject, marks FROM grades WHERE roll_no = ?", (roll_no,))
    rows = cur.fetchall()

    total = 0
    for subject, marks in rows:
        total += marks

    average = total / len(rows)

    if average >= 90:
        grade_letter = "A+"
    elif average >= 75:
        grade_letter = "A"
    elif average >= 60:
        grade_letter = "B"
    elif average >= 40:
        grade_letter = "C"
    else:
        grade_letter = "F"