Desktop app with C#

Question

how to send and recieve data from a desktop app to arduino and arduino to app

Answer 1

1 serial via usb
2 serial via bluetooth
3 socket connection via ethernet shield
4 socket connection via wifi shield
5 http rest requests sent from the c# program to a Server on the arduino.
6 Serial on the audio out
7 Audio Morse code
9 DTMF audio signals
10 IR blaster on comp serial port tx receiver on rx pin of the arduino
11 sms control (using a 3G modem on the computer and a gsm module on the arduino)
more...

Answer 2

Open arduino's Faq's and guides