...And by the way, you need to make the buffer unsigned char, not int. You are reading bytes from the sensor, not 32 bit integers.

I am having problems of my own with the same compass sensor and I am getting to the point, where I believe, that my sensor is broken. I get random values for x,y,z, jumping up and down between seemingly random values, no matter how I rotate the sensor. I have tried your code + other code with no luc...