求随机生成一个字符串写法解决方案

求随机生成一个字符串写法
刚自己写了一下,每次都不能生成唯一的数字.有重复
所以恳请大家帮忙
需求是:共12位字符,前四位为字母,后四位为数字!

[解决办法]

C# code

                Random ran=new Random();                string s="";                int num=0;                int i=0;                do                {                    num=ran.Next(1,34);                    if(s!="")                    {                        if(s.IndexOf(num.ToString()+",")==0)                        {                                                }                        else if(s.IndexOf(","+num.ToString()+",")>0)                        {                                                }                        else                        {                            s+=num.ToString()+",";                            i++;                        }                    }                    else                    {                        s+=num.ToString()+",";                        i++;                    }                }while(i!=6);                Response.Write(s);
[解决办法]
 int number;
       char code;
       string checkCode = String.Empty;

       System.Random random = new Random();

       for (int i = 0; i < 4; i++)
       {
           number = random.Next();

           if (number % 2 == 0)
           {
               code = (char)('0' + (char)(number % 10));
               checkCode += code.ToString();
           }
           else
           {
               i--;
           }
       }
       for (int j = 0; j < 4; j++)
       {
           number = random.Next();
           if (number % 2 != 0)
           {
               code = (char)('A' + (char)(number % 26));
               checkCode += code.ToString();
           }
           else
           {
               j--;
           }
       }
       Response.Write(checkCode.ToString());
[解决办法]
要求不高的话,直接拿系统随机返回的字串就可以了.


C# code
    public static string getRndString(int len)    {        return System.Guid.NewGuid().ToString().Substring(0, len);       }    string x = getRndString(6);
[解决办法]
        private string getString()
       {
           string str = "a,b,c,d,e,f,g,h,i,j,k,l,m,n,p,q,r,s,t,u,v,w,x,y,z";
           string strString = null;
           string strNumber = null;
           string[] strs = str.Split(',');
           Random rand = new Random();
           for (int i = 0; i < 4; i++)
           {
               strString += strs[rand.Next(25)].ToString();
               strNumber += rand.Next(10).ToString();
           }

           return strNumber + strString;
       }