Grove Temperature&Humidity Sensor Pro

[schmron]

#define DHT11_PIN 0

You define digital port 0.
DHT communicate digital, not analog. If you want to use analog port use its digital portnumber (A0 = 14).

instructables.com/id/How-to- … ith-no-ex/

arduino.cc/en/Tutorial/AnalogInputPins
arduino.cc/en/Tutorial/DigitalPins

edit
Use a library like this:
github.com/adafruit/DHT-sensor-library
or
arduino.cc/playground/Main/DHT11Lib