PID Control Object (with questions)

Great to see you testing the code.

You really should not be setting internal parts of the library - ctr.out=0.0;

At this point - you could call ctr.compute(); if you have set a value for input. There is a ctr.setOutput(x) - however this is intended to be used if the controller in manual mode.

Same goes for getting the output ctr.getOutput(). If the internal implementation of the library was changed and internal vars renamed (i.e. perhaps shorted to save space), your code could break...