Debug printing help

I want to add some debug prints in the lower level code, such as in wiring_analog.c, etc.

Is there an API that I can use to print the serial monitor port? I tried using Serial.print, but this failed to compile.

bit-banger:
I want to add some debug prints in the lower level code, such as in wiring_analog.c, etc.

That code is already pretty well debugged.

Please PROPERLY post the code that failed to compile. For example, use code tags please.