订单号生成规则，谁用谁知道

class Program
    {
        //订单号数据源，实际项目中，这里是从数据库中读取过来的
        string[] strList = { "201512000001", "201512000002", "201512000003", "201512000004", 
                             "201512000008", "201512000007", "201512000006", "201512000005", 
                             "201512000009", "201512000010", "201512000011", "201512000012",
                             "201512000013","201512000014","201512000015" };        
        static void Main(string[] args)
        {
            Program p = new Program();
            Console.WriteLine(p.GetOrderNum());
            Console.ReadKey();
        }

        public string GetOrderNum()
        {
            string result = "";            
            string YearMonth = DateTime.Now.ToString("yyyyMM");
            var count = Count(YearMonth);//201512  5
            result = YearMonth + "0000001";
            var dd = count.ToString().Length;
            switch (dd)
            {
                case 1:
                    result = YearMonth + "00000" + (count + 1);
                    break;
                case 2:
                    result = YearMonth + "0000" + (count + 1);
                    break;
                case 3:
                    result = YearMonth + "000" + (count + 1);
                    break;
                case 4:
                    result = YearMonth + "00" + (count + 1);
                    break;
                case 5:
                    result = YearMonth + "0" + (count + 1);
                    break;
                default:
                    result = YearMonth + (count + 1);
                    break;
            }
            return result;
        }
        
        public int Count(string yearMonth) {
            int result = 0;
            result = strList.Count(item=>item.Contains(yearMonth));
            return result;
        }       
    }

用string.PadLeft(n,'0')补零写出来的代码要比上面if的要好看很多，多谢园友提醒，最终代码请看下面

public string GetOrderNum2()
{
string result = "";
string YearMonth = DateTime.Now.ToString("yyyyMM");
var count = Count(YearMonth);//201512 5 
result= YearMonth+(count + 1).ToString().PadLeft(6,'0');
return result;
}

　　

谁有更好的生成规则，不妨一起讨论下