生成随机数 纯数字，纯字母，数字+字母

/// <summary>
/// 生成随机纯字母随机数
/// </summary>
/// <param name="IntStr">生成长度</param>
/// <returns></returns>
public static string Str_char(int Length)
{
    return Str_char(Length, false);
}
/// <summary>
/// 生成随机纯字母随机数
/// </summary>
/// <param name="Length">生成长度</param>
/// <param name="Sleep">是否要在生成前将当前线程阻止以避免重复</param>
/// <returns></returns>
public static string Str_char(int Length, bool Sleep)
{
     if (Sleep)
     System.Threading.Thread.Sleep(3);
     char[] Pattern = new char[] { '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 result = "";
     int n = Pattern.Length;
     System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));
     for (int i = 0; i < Length; i++)
        {
            int rnd = random.Next(0, n);
            result += Pattern[rnd];
        }
     return result;
}
/// <summary>
/// 生成随机纯字母随机数
/// </summary>
/// <param name="Length">生成长度</param>
/// <param name="Sleep">是否要在生成前将当前线程阻止以避免重复</param>
/// <returns></returns>
public static string Str_charSamll(int Length, bool Sleep)
{
    if (Sleep)
    System.Threading.Thread.Sleep(3);
    char[] Pattern = new char[] { '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 result = "";
    int n = Pattern.Length;
    System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));
    for (int i = 0; i < Length; i++)
    {
        int rnd = random.Next(0, n);
        result += Pattern[rnd];
    }
    return result;
}