I want to connect an Android phone/tablet to an Arduino.  I only want to send/receive bytes; the Android app would receive and send the bytes.  What is out there that I can use (libraries, etc.)?  No rooting the phone/tablet, since I want to accommodate most/many generic tablets.  Also, avoiding using a USB Host shield would be preferable.

Thank you senti, you helped me connect the dots.

I finally figured out that I need both a sketch that needs to be uploaded to the Arduino, that will handle Serial communication and act upon that serial communication (i.e. flash an LED when a byte is sent).  From the computer C++ code, I can then send information via Serial to the Arduino.  In my searches, I had always found either Arduino code to receive serial information or C++ code to send serial information separately, but did not understand that you needed both.

I can easily make the Arduino flash using Arduino code or the example sketch.

I am talking about making the Arduino LED flash from C++, not via a sketch.  I want to specify some input pin to receive a flashing signal from C++.

Also, yes I believe Windows is different from Linux in the way that it opens and communicates with ports.  I would assume that a library would have different code to open a port in Windows than a port in Linux.

I am currently working on flashing an LED connected to one of the pins on my Arduino.  I would like it to do it from C++ for Windows and Android.
Does anyone have any tips on what I should do?  Right now, I only want an LED to flash, but eventually I want it to send/receive bytes from the Arduino.