iOS Saving application state

Im having a little trouble figureing out how to save simple instance variables to a file in order to save my application state.

I have figured out how to read and write data with Archivers, but this requires objects to be sent to the data archiver via an Array.

The only thing i need to do to save my application state is save two double instance variable and one boolean instance variable and them simply reinitialize them when the application is run again.

How would i go about saving these double and boolean values with an archiver?

well i cheated and just converted the doubles and bool value into an NSString object and put those into an array and sent the array to the archiver.

Just more work when i read the strings i need to convert them back to double and bool.

Any better way to do this?