S = Sum(Ai * Wi), i = 0, ... , 16 ，先对前17位数字的权求和
Ai:表示第i位置上的身份证号码数字值
Wi:表示第i位置上的加权因子
Wi: 7 9 10 5 8 4 2 1 6 3 7 9 10 5 8 4 2
（2）计算模
Y = mod(S, 11)
（3）通过模得到对应的校验码
Y: 0 1 2 3 4 5 6 7 8 9 10
校验码: 1 0 X 9 8 7 6 5 4 3 2
四、举例如下：
北京市朝阳区: 11010519491231002X
广东省汕头市: 440524188001010014
以下是程序代码：
private string CheckCidInfo(string cid)
{
string[] aCity = new string[]{null,null,null,null,null,null,null,null,null,null,null,"北京","天津","河北","山西","内蒙古",null,null,null,null,null,"辽宁","吉林","黑龙江",null,null,null,null,null,null,null,"上海","江苏","浙江","安微","福建","江西","山东",null,null,null,"河南","湖北","湖南","广东","广西","海南",null,null,null,"重庆","四川","贵州","云南","西藏",null,null,null,null,null,null,"陕西","甘肃","青海","宁夏","新疆",null,null,null,null,null,"台湾",null,null,null,null,null,null,null,null,null,"香港","澳门",null,null,null,null,null,null,null,null,"国外"};
double iSum=0;
string info="";
System.Text.RegularExpressions.Regex rg = new System.Text.RegularExpressions.Regex(@"^\d{17}(\d|x)$");
System.Text.RegularExpressions.Match mc = rg.Match(cid);
if(!mc.Success)
{
return "";
}
cid = cid.ToLower();
cid = cid.Replace("x","a");
if(aCity[int.Parse(cid.Substring(0,2))]==null)
{
return "非法地区";
}
try
{
DateTime.Parse(cid.Substring(6,4)+"-"+cid.Substring(10,2)+"-"+cid.Substring(12,2));
}
catch
{
return "非法生日";
}
for(int i=17;i>=0;i--)
{
iSum +=(System.Math.Pow(2,i)%11)*int.Parse(cid[17-i].ToString(),System.Globalization.NumberStyles.HexNumber);
}
if(iSum%11!=1)
return("非法证号");
return(aCity[int.Parse(cid.Substring(0,2))]+","+cid.Substring(6,4)+"-"+cid.Substring(10,2)+"-"+cid.Substring(12,2)+","+(int.Parse(cid.Substring(16,1))%2==1¡"男":"女"));
}