Sorry, but I think that you really have to pause and read a tutorial on pointers. You need to understand how to work with pointers before you can proceed. At the moment, it looks like you have been making changes to your code without the faintest clue of why I have been suggesting what I have been suggesting.
Oh, I did not notice that in your post #23, you changed your correct line of code to:
which is not correct. If area, radius and volume are pointers, what are they supposed to point to? Again, this means that you need to understand the concept of a pointer and how to use pointers effectively.Code:double *area, *radius, *volume;