C# 通过身份证查询出生日期

private int GetAgeBycode(string b_car_code)
        {
            string birthday = "";
            //处理18位的身份证号码从号码中得到生日和性别代码
            if (b_car_code.Length == 18)
            {
                birthday = b_car_code.Substring(6, 4) + "-" + b_car_code.Substring(10, 2) + "-" + b_car_code.Substring(12, 2);
            }
            //处理15位的身份证号码从号码中得到生日和性别代码
            if (b_car_code.Length == 15)
            {
                birthday = "19" + b_car_code.Substring(6, 2) + "-" + b_car_code.Substring(8, 2) + "-" + b_car_code.Substring(10, 2);
            }
            return birthday;

        }