Where can I see the output of printf?
If you're working with the standard Arduino environment and libraries then printf() won't display anything anywhere. The reason is that microcontrollers could be connected to any number of different output/communication devices in any way. stdio would have no idea how or where to send the data.

The most common approach to outputting text from an Arduino (particularly during development) is to send it to the primary UART port using Serial.begin() and Serial.print(). If the Arduino is connected to your computer via USB then the Arduino IDE's serial monitor should display the result.

If you really want to use printf() though then it is possible to make it work (or implement similar functionality). A full explanation is on this page:


http://playground.arduino.cc/Main/Printf