随机数生成

一个小小的随机数生成

        /// <summary>
        /// lou 2019-9-25 15:14:02 生成随机字符串
        /// </summary>
        /// <param name="length">返回值的长度</param>
        /// <param name="type">返回值类型，1：纯数字；2：小写字母；3：大写字母；4：大小写字母混合；5：小写字母和数字混合；6：大写字母和数字混合；7：大小写字母和数字混合</param>
        /// <returns></returns>
        public static string getcode(int length, int type)
        {
            string str = "0123456789abcdefghigklmnopqrstuvwxyzabcdefghigklmnopqrstuvwxyz";
            string retstr = "";
            random rnd = new random(getrandomseed());
            for (int i = 0; i < length; i++)
            {
                switch (type)
                {
                    case 1:
                        retstr += rnd.next(10).tostring();
                        break;
                    case 2:
                        retstr += str.substring(10 + rnd.next(26), 1);
                        break;
                    case 3:
                        retstr += str.substring(36 + rnd.next(26), 1);
                        break;
                    case 4:
                        retstr += str.substring(10 + rnd.next(52), 1);
                        break;
                    case 5:
                        retstr += str.substring(0 + rnd.next(36), 1);
                        break;
                    case 6:
                        retstr += str.substring(0 + rnd.next(36), 1).toupper();
                        break;
                    case 7:
                        retstr += str.substring(0 + rnd.next(61), 1);
                        break;
                }
            }
            if (retstr == "")
            {
                retstr = getcode(length, type);
            }
            return retstr;
        }
        /// <summary>
        /// 描 述:创建加密随机数生成器 生成强随机种子
        /// </summary>
        /// <returns></returns>
        private static int getrandomseed()
        {
            byte[] bytes = new byte[4];
            rngcryptoserviceprovider rng = new rngcryptoserviceprovider();
            rng.getbytes(bytes);
            return bitconverter.toint32(bytes, 0);
        }