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", "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 "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;
}