Oh dear..... PC programmer, you're not in Kansas any more.
Regular Arduinos do have float and double but they are the same 32-bit IEEE floating point (6 to 7 places "accuracy") that is computed without an FPU (is slowww). Your BEST BET is to ditch floating point and work in integers which for you probably means a bit of discovery and invention. If you are/were good at math concepts it should be relatively easy. If not then chances are you'll stick with float and either accept the error or torture your code into correcting for the round-offs like so many others.
Regular Arduinos have very little RAM. For example, UNO has 2048 BYTES of RAM. MEGA has 8196. If you use wasteful practices like C++ Strings and/or other Container classes then expect to crash once you get beyond trivial code. That 2k is for both heap and stack which, do they still teach about those or is hardware a non-subject?
Regular Arduinos have no operating system. You put your own bugs in, but you can import libraries and code examples to occasionally save time there. There used to and still may be bumps in the heap management too, I can't say since I avoid deallocation like the plague.
Your Arduino IDE comes with Libraries and Example programs fit to whatever version it is. The Arduino main site has pages just covering those (you would do well surfing the site and bookmarking entry points because you WILL need to refer to them, be sure to get this one too: http://www.nongnu.org/avr-libc/user-manual/modules.html
If you have to have main() then you can but the IDE is set up to put you inside of main. You may know C++ but there are concepts you clearly have not picked up yet. Here is a good link to start, don't blow it off:http://arduino.cc/en/Tutorial/Foundations#.Uw8280gz3jI
Spend time with the Examples. They are not perfect, especially the ones that use Strings, but they work. They were written by modern PC programmers.
Learn Blink Without Delay sooner than later. It is at the heart of real time code and interleaved tasking. If you want to 'do more than one thing at a time' then you need BWD.
Get through all that and you will be able to ask much better questions and save yourself much time.
Next time we might be able to talk about finite state machines.