Operator for check two conditions

I want to check two statements in one if statement. Maybe for you its a easy question!

I have the following code written:

var roommatch = reservations.FirstOrDefault(p => p.roomnumber == Convert.ToInt32(kamercomboBox.SelectedItem.ToString()));
var datematch = reservations.FirstOrDefault(p => p.date == date);    
if (roommatch == null && datematch == null)
            {
                reservations.Add(new Reservation(multiplenames, lastnameTextBox.Text, gendercomboBox.SelectedText, Convert.ToInt32(ageNumericUpDown.Value), Convert.ToInt32(kamercomboBox.SelectedItem.ToString()), Convert.ToInt32(quantityUpDown.Value), date));
            }

With this i check the date and roomnumber

But now i need something which checks of i can reserve a room on another date.