who can help me c what problem? asp C#

Question

int Correct = Convert.ToInt32(Session["Correct"].ToString());

int total = Convert.ToInt32(Session["Wrong"].ToString()) + Convert.ToInt32(Session["Correct"].ToString());

  double dbMark = 100 * correct / total;

   Response.Write("    " + total.ToString() + "      " + dbMark.ToString());

when i run my problem can not function ~