How to check for double checkbox IsChecked in if statement ? C#, WPF

How can I check for 2 or more checkBox IsChecked values inside single if statement in WPF C# ? I am trying to do like this but its not working.

 if ((symbols_cb.IsChecked ?? true) && (digits_cb.IsChecked ?? true))
 {
        MessageBox.Show("Check - Yes it is selected.");
 }

Here symbols_cb and digits_cb are check box and I want a message to be displayed while both the checkbox has been selected.