Calculating percentage and final score of an ASP.NET online examination website

    protected void Page_Load(object sender, EventArgs e)
    {
        SqlCommand com = new SqlCommand("Select * from [Biology]", con);
        SqlDataAdapter da = new SqlDataAdapter(com);
        DataTable dt2 = new DataTable();
        da.Fill(dt2);
        grdquestions.DataSource = dt2;
        grdquestions.DataBind();


    }

    protected void examsubmit_Click(object sender, EventArgs e)
    {
        SqlCommand com = new SqlCommand("Select * from [Biology]", con);
        SqlDataAdapter da = new SqlDataAdapter(com);
        DataTable dt = new DataTable();
        da.Fill(dt);

    int correctAnswers = 0, incorrectAnswers = 0,
    totalMarks = 0, totalQuestions = grdquestions.Rows.Count;

  for (int i = 0; i < totalQuestions; i++)
    {
    GridViewRow row = grdquestions.Rows[i];
    string answer = dt.Rows[i]["Answer"].ToString();
    int marks = Convert.ToInt32(dt.Rows[i]["Marks"]);
    var radioButtons = new List<radiobutton>
    {
        (RadioButton)row.FindControl("rdOption1"),
        (RadioButton)row.FindControl("rdOption2"),
        (RadioButton)row.FindControl("rdOption3"),
        (RadioButton)row.FindControl("rdOption4"),
    };

    foreach (var radioButton in radioButtons)
    {
        if (radioButton.Checked)
        {
            if (radioButton.Text == dt.Rows[i]["Answer"].ToString())
            {
                correctAnswers++;
                totalMarks += marks;
            }
            else
            {
                incorrectAnswers++;
                radioButton.Checked = false;
            }
        }
        else if (radioButton.Text == dt.Rows[i]["Answer"].ToString())
        {
            correctAnswers++;
            radioButton.Checked = true;
            
        }
    }
}

Label2.Text = "FinalScore is :" + totalMarks;

string correctAnswerPercentage = (correctAnswers / totalQuestions).ToString("0.00%");
Label2.Text = "Percentage is "+correctAnswerPercentage;
    }
}