Need some help in arduino robot

I want to collect the robot heading degree from the compass, here is an example code:

#include <ArduinoRobot.h>

void setup(){
Robot.begin();
Serial.begin(9600);
}

void loop(){
int compass = Robot.compassRead();
Serial.println(compass);
delay(100);
}

However, when I open the serial monitor, nothing shows on the monitor, thus how can I transfer the compass data to laptop through serial port?

Thank you!