While you are programming in a 'high level language' such as C (and I'll avoid the discussion about whether C really is a high level language) you need to think in the way it was intended to be used - it was created to write an operating system which talked directly to the hardware registers and do very basic tasks and that is what you need to do when programming embedded devices. the Family Reference Manuals or FRM) that have examples. You need to understand at a very low level what you are trying to do and the data sheet will tell you everything (if you dig around a bit - sometimes they can be overwhelming to start with) and there are other documents for some of the other device families (e.g. The discussion about TRIS, LAT and PORT registers exemplifies this. This brings up my final point: you need to think at the 'bare metal' level with embedded devices. Assuming you want to use a UART, then once you have initialised it - typically 10 or so lines to set the various bits in the configuration registers and enabled the peripheral - then to actually send the character is a single assignment to an internal 'special function register' (SFR). To continue your example, you need to know how the characters you have generated are to be displayed: on a LCD or via a serial line to another computer or whatever. Where microcontrollers shine is that they have lots of built-in peripherals that let you get close and direct access to the required functionality. Some compiler libraries do provide equivalents but even there, they typically rely on you providing a function (often 'putchar') to do the actual output.

Further, by default there are no standard IO streams. It is MUCH faster to simply call the function yourself. Even in your example, the format string never changes and so the 'printf' statement will spend a lot of time at runtime parsing it and working out what to do, only to call the same functions (something like 'ftoa' in your example). They take up a LOT of memory and are slow at runtime.

(Note that some compilers want the main to return an int in which case you add the necessary parts to the code but that is just to avoid the warnings: an embedded program should NEVER stop.) 'printf' and other members of the family are rarely if ever used.

For a start embedded systems have no operating system around them - therefore there is nothing for the 'main' function to return to. Knowing C very well is a good thing BUT, as your very first post in this thread demonstrates, you need to start thinking about embedded systems which have very limited memory (both RAM and ROM) and requires a different way of thinking.

Programming pic microcontroller