生成验证码方法

/// <summary>
/// 封装n位验证码的方法 不生成1,l 0,o等字符串;
/// </summary>
/// <param name="len">验证码长度 一般4-6位</param>
/// <returns></returns>

 public static string GenerateCaptchaCode(int len)
         {
             //组成验证码的字符
             char[] date = { \'a\', \'c\', \'d\', \'e\', \'f\', \'g\', \'k\', \'m\', \'p\', \'r\', \'s\', \'t\', \'w\', \'x\', \'y\', \'3\', \'4\', \'5\', \'7\', \'8\' };
             StringBuilder sbCode = new StringBuilder();
             Random rand = new Random();
             for (int i = 0; i < len; i++)
             {
                 char ch = date[rand.Next(date.Length)];//[0,date.Length]范围
                 sbCode.Append(ch);
             }
             return sbCode.ToString();
         }