c# 版 18位身份证严格验证及 15位转18位

private string GetCard(string cid)
        {
            if (cid.Length == 15)
            {
                cid = per15To18(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","***",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 "格式不正确!";
                return "";
            }
            cid = cid.ToLower();
            cid = cid.Replace("x","a");
            if(aCity[int.Parse(cid.Substring(0,2))]==null)
            {
                //return "非法地区";
                return "";
            }
            try
            {
                 DateTime.Parse(cid.Substring(6,4)+"-"+cid.Substring(10,2)+"-"+cid.Substring(12,2));
            }
            catch
            {
                 //return "非法生日";
                 return "";
            }
            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("");

            return(cid.Substring(6,4)+"-"+cid.Substring(10,2)+"-"+cid.Substring(12,2));

        }

private string per15To18(string perIDSrc)
        {
            int iS = 0;

            //加权因子常数
            int[] iW = new int[] { 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2 };
            //校验码常数
            string LastCode = "10X98765432";
            //新身份证号
            string perIDNew;

            perIDNew = perIDSrc.Substring(0, 6);
            //填在第6位及第7位上填上‘1’，‘9’两个数字
            perIDNew += "19";
            perIDNew += perIDSrc.Substring(6, 9);
            //进行加权求和
            for (int i = 0; i < 17; i++)
            {
                iS += int.Parse(perIDNew.Substring(i, 1)) * iW[i];
            }

            //取模运算，得到模值
            int iY = iS % 11;
            //从LastCode中取得以模为索引号的值，加到身份证的最后一位，即为新身份证号。
            perIDNew += LastCode.Substring(iY, 1);

            return perIDNew;
        }

转载他处，地址不详，以备不时之需。