How to check Strong Password

public static bool IsPasswordStrong(string password)
{
  // Check for strong password
  return Regex.IsMatch(password, @"^(?=.{8,})(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?!.*\s).*$");
}


protected void cmdSubmit_Click(object sender, EventArgs e)
{
        string strtxtNewPwd = txtNewPwd.Text;
        if (IsPasswordStrong(strtxtNewPwd) == false)
        {
            errorpanel.Style.Add(HtmlTextWriterStyle.Display, "inline");
            status.Text = "Password must be atleast 8 characters long and should be a mix of atleast One Uppercase letter, One Lowercase letter and One Numeral.";
        }
        else
        {
            // Update password
        }
}



Guidelines for creating strong password 
Be at least eight characters long. Because of the way passwords are encrypted, the most secure passwords are 8 or 14 characters long.
Contain at least one character from the following three groups:

Group  Examples 
Uppercase Letters  A,B,C... 
Lowercase Letters  a,b,c... 
Numerals  0,1,2,3,4,5,6,7,8,9 

Be significantly different from prior passwords.
Not contain your name or user name.
Not be a common word or name.
Exapmle:- Password1  => (P)Uppercase, (assword)Lowercase, (1)Numeral