c#验证身份证号

using System;
using System.Collections.Generic;
using System.Text;

namespace IDprocess
{
class Program
{
static void Main(string[] args)
{
Console.Write("请输入身份证号：");
string idnumber = Console.ReadLine().Trim();
ID oneID = new ID(idnumber);
if (oneID.IsValid())
Console.WriteLine("您的出生日期是：" + oneID.getBirthday().ToString("yyyy年M月d日"));
else
Console.WriteLine("对不起，身份证号码错误！");
Console.Read();
}
}
class ID
{
private string IDnumber;
public ID(string idnumber)
{
this.IDnumber = idnumber.Trim();
}
//判断是否为有效的身份证号码：
public bool IsValid()
{
int year, month,day ;
if (IDnumber.Length == 15)
{
for (int i = 0; i < 15; i++)
{
//如果有非数字，则无效，返回false
if (!char.IsNumber(IDnumber[i]))
{
return false;
}
}
//取得出生年月日：
year = Int32.Parse("19" + IDnumber.Substring(6, 2));
month = Int32.Parse(IDnumber.Substring(8, 2));
day = Int32.Parse(IDnumber.Substring(10, 2));
//调用方法IsValidBirthday判断是否为有效的出生年月日：
return IsValidBirthday(year, month, day);
}
else if (IDnumber.Length == 18)
{
for (int i = 0; i < 17; i++)
{
if (!char.IsNumber(IDnumber[i]))
{
return false;
}
}
if (!char.IsNumber(IDnumber[17]) && IDnumber[17] != 'X')
return false;
//取得出生年月日：
year = Int32.Parse(IDnumber.Substring(6,4));
month = Int32.Parse(IDnumber.Substring(10, 2));
day = Int32.Parse(IDnumber.Substring(12, 2));
//调用方法IsValidBirthday判断是否为有效的出生年月日：
return IsValidBirthday(year, month, day);
}
else
return false;
}
//判断是否为有效的出生年月日：
private bool IsValidBirthday(int year,int  month,int day)
{
if(year==0)
return false;
if (month<1||month > 12)
return false;
//判断天数是否在指定年和月中所限制的天数范围之内。
if (day < 1 || day > DateTime.DaysInMonth(year, month))
return false;
//判断出生日期是否大于现在的日期。
DateTime Birthday = new DateTime(year, month, day);
if (Birthday > DateTime.Now)
return false;
return true;
}
//获取出生日期
public DateTime getBirthday()
{
DateTime  Birthday;
int year, month,day ;
if (IsValid())
{
if (IDnumber.Length == 15)
{
year = Int32.Parse("19" + IDnumber.Substring(6, 2));
month = Int32.Parse(IDnumber.Substring(8, 2));
day = Int32.Parse(IDnumber.Substring(10, 2));
Birthday = new DateTime(year, month, day);
}

else
{
year = Int32.Parse(IDnumber.Substring(6, 4));
month = Int32.Parse(IDnumber.Substring(10, 2));
day = Int32.Parse(IDnumber.Substring(12, 2));
Birthday = new DateTime(year, month, day);
}
}
else Birthday = new DateTime(1, 1, 1);
return Birthday;
}
}
}