RndNum 生成随机字符串，包含数字和小写字母

  /// <summary>
  /// 生成随机字符串，包含数字和小写字母
  /// </summary>
  /// <param name="VcodeNum">字符串长度</param>
  /// <returns></returns>
  public static string RndNum(int VcodeNum)
  {
   string Vchar="0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p"+
    ",q,r,s,t,u,v,w,x,y,z";
   string[] VcArray=Vchar.Split(new Char [] {','});
   string VNum="";
   int temp=-1;

   Random rand=new Random();
  
   for(int i=1;i<VcodeNum+1;i++)
   {
    if(temp!=-1)
    {
     rand=new Random(i*temp*unchecked((int)DateTime.Now.Ticks));
    }
  
    int t=rand.Next(VcArray.Length);
    if(temp != -1 && temp == t)
    {
     return RndNum(VcodeNum);
    }
    temp=t;
    VNum+=VcArray[t];
   }
   return VNum;
  }