Is there a way to “grow” my array as my program continues?

Question

I am creating a prime generator in c++ using an array to store primes as I find them and then use them to check against potentials later. Is there a way to "grow" my array as my program continues?

Answer 1

See std:vector. http://new.cplusplus.com/reference/stl/vector/

Answer 2

I would use a std:vector something like this:

vector<int> primes;

then you would add primes to it by using:

primes.push_back(2);

and retrieve values from the vector by using:

primes[0];

Good luck!

Answer 3

You could use a std::vector template, and use the reserve method based on an upper-bound for the prime counting function.

Answer 4

It sounds like you need a vector to store primes in.

Answer 5

I think your best bet is probably a std::list; whereas a vector needs to reallocate previously stored items when its reserved space is exceeded, this doesn't happen with a list.

Answer 6

The usual cases where this sort of need arises also require an efficient lookup operation. My experience is to go for std::map which makes life much easier than vectors here.

Answer 7

If there is any initially known limit to which you are going to go, you can just calculate the length of the array you need with this simple formula:

let N is that limit and LENGTH is the needed length of the array, so

LENGTH = N / log(N)

where the log(N) is a natural logarithm of N

for more information, see: Prime number distribution theorem.