过滤非法字符

using System;
using System.Text.RegularExpressions;

class Test
{
  static void Main()
  {
    Regex r = new Regex("admin|super|root");
    string username = "I_am_admin";
    if (r.IsMatch(username))
    {
      Console.WriteLine("不合法的用户名");
    }
  }
}