protected void Page_Load(object sender, EventArgs e)
{
  string str = "11010519491231002X";
  bool result = CheckCardId(str);
  if (result == true)
  {
    Response.Write("Yes!");
  }
  else
  {
    Response.Write("No!");
  }
}
  
/// <summary>
/// 驗證身份證是否正確 
/// </summary> 
/// <param name="str"></param> 
/// <returns></returns> 
private static bool CheckCardId(string str)
{
  string number17 = str.Substring(0, 17);
  string number18 = str.Substring(17);
  string check = "10X98765432";
  int[] num = { 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2 };
  int sum = 0;
  for (int i = 0; i < number17.Length; i++)
  {
    sum += Convert.ToInt32(number17[i].ToString()) * num[i];
  }
  sum %= 11;
  if (number18.Equals(check[sum].ToString(), StringComparison.OrdinalIgnoreCase))
  {
    return true;
  }
  else
  {
    return false;
  }
}