The code continues...

Ok, its definately less than perfect, but its a good start.
Using the gotoxy() function, I've got it to display the rough position of the 'planet' on the screen. It doesn't show the sun but it's assumed that is at the center.
The numbers are the number of seconds left of the simulation. It starts at 70, but they overwrite each other.
It's worked better than I expected. Now I need to put a slight delay on the while loop so that I can see it's progress better. Then I'll research into graphics programs.