验证码制作之二: 可选择位数的字符与数字混合码

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

/// <summary>
/// randomCode 的摘要说明
/// </summary>
public class randomCode
{
 public randomCode()
 {
  //
  // TODO: 在此处添加构造函数逻辑
  //
 }
    /// <summary>
    /// 验证码
    /// </summary>
    /// <param name="n">验证码的个数</param>
    /// <returns>返回生成的随机数</returns>
    public string RandomNum(int n) //
    {
        string strchar =     "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,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 = strchar.Split(',');
        string VNum = "";                    //
        int temp = -1;                       //记录上次随机数值，尽量避免产生几个一样的随机数
                                             //采用一个简单的算法以保证生成随机数的不同
        Random rand = new Random();
        for (int i = 1; i < n + 1; i++)
        {
            if (temp != -1)
            {
                rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
            }
            int t = rand.Next(61);
            if (temp != -1 && temp == t)
            {
                return RandomNum(n);
            }
            temp = t;
            VNum += VcArray[t];
        }
        return VNum;//返回生成的随机数
    }
}