GPSTester | GPS tester for Android ROMs | Android library

There are three issues with the code that stand out to me. First is that you overwrite the first two parameters a1 and a2. Whatever is passed to the function is being lost. Second, the Serial.print(bearing) call is unreachable code, and would never be called even if it were not throwing a compiler error.

A quick internet search of "Arduino Serial print" found descriptions of a method that will take integers and floats and send an ASCII representation of the values over a serial connection. I am guessing this is the function you are using.

However, you function call is trying to pass a pointer to a function to the Serial.print() call instead of a float or integer value. If your desire is to print the results of the call to bearing out to the serial link, you should be doing so with the return value of the function, not in the function itself with a pointer to the function.

Somewhere in your code you are going to call bearing. I suspect you want it to look like this:

Serial.print(bearing(a1,a2,deg,degy));

This will make the call to bearing with the desired parameters, and then send the result to the serial port.