photoresistor

const byte analogInPin = A0;  // Analog input pin that the potentiometer is attached to

void setup() {
  // initialize serial communications at 9600 bps:
  Serial.begin(9600);
}

void loop() {
  Serial.print("sensor = ");
  Serial.print(analogRead(analogInPin));
  // wait 2 milliseconds before the next loop for the analog-to-digital
  // converter to settle after the last reading:
  delay(2);
}

If your photoresistor is connected to a different analog pin you just need to change the definition of analogInPin.