CppLearning/EssentialCpp/chap2_5.cpp

#include "utils.h"
#include <limits>

bool is_size_ok(int size) {
	if (size <= 0 || size > 1024) {
		cout << "size is invalid!" << endl;
		return false;
	}
	else {
		return true;
	}
}

vector<u32>* fibon_seq(int size) {
	static vector<u32> elems;

	if (!is_size_ok(size)) {
		return 0;
	}


	int current_size = elems.size();

	if (size > current_size) {
		for (int ix = current_size; ix < size; ++ix) {
			if (ix < 2) {
				elems.push_back(1);
			}
			else {
				int value_ix = elems[ix - 1] + elems[ix - 2];
				elems.push_back(value_ix);
			}

		}
	}

	return &elems;

}

bool fibon_elem(int position, u32& elem) {

	vector<u32>* fibon_vector = fibon_seq(position);
	if (fibon_vector) {
		elem = (*fibon_vector)[position-1]; //index overflow
		return true;
	}
	else {
		elem = 0;
		return false;
	}

}


int main() {
	u32 elem = 0;
	bool ret = fibon_elem(100, elem);
	if (ret) {
		cout << "elem is" << elem << endl;
	}

	return 0;
}