/// <summary>
/// 密码强度
/// </summary>
private enum Strength
{
 Invalid = 0, //无效密码
 Weak = 1, //低强度密码
 Normal = 2, //中强度密码
 Strong = 3 //高强度密码
};
/// <summary>
/// 计算密码强度
/// </summary>
/// <param name="password">密码字符串</param>
/// <returns></returns>
private static Strength PasswordStrength(string password)
{
 //空字符串强度值为0
 if (password == "") return Strength.Invalid;
 //字符统计
 int iNum = 0, iLtt = 0, iSym = 0;
 foreach (char c in password)
 {
  if (c >= '0' && c <= '9') iNum++;
  else if (c >= 'a' && c <= 'z') iLtt++;
  else if (c >= 'A' && c <= 'Z') iLtt++;
  else iSym++;
 }
 if (iLtt == 0 && iSym == 0) return Strength.Weak; //纯数字密码
 if (iNum == 0 && iLtt == 0) return Strength.Weak; //纯符号密码
 if (iNum == 0 && iSym == 0) return Strength.Weak; //纯字母密码
 if (password.Length <= 6) return Strength.Weak; //长度不大于6的密码
 if (iLtt == 0) return Strength.Normal; //数字和符号构成的密码
 if (iSym == 0) return Strength.Normal; //数字和字母构成的密码
 if (iNum == 0) return Strength.Normal; //字母和符号构成的密码
 if (password.Length <= 10) return Strength.Normal; //长度不大于10的密码
 return Strength.Strong; //由数字、字母、符号构成的密码
}

static void Main(string[] args)
{
 string sPassword;
 while (true)
 {
  Console.WriteLine("请输入一个密码：");
  sPassword = Console.ReadLine();
  switch (PasswordStrength(sPassword))
  {
   case Strength.Invalid: Console.WriteLine("无效密码\n"); break;
   case Strength.Weak: Console.WriteLine("低强度密码\n"); break;
   case Strength.Normal: Console.WriteLine("中强度密码\n"); break;
   case Strength.Strong: Console.WriteLine("高强度密码\n"); break;
  }
 }
}