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;
 }
}