EssentialCplusplus/2.2.cpp at master · aiilab/EssentialCplusplus · GitHub

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#include <iostream>
#include <string>
#include <vector>
#include <fstream>

using namespace std;

bool calc_elements(vector<int> &vec, int pos);
void display_elems(vector<int> &vec, const string &title, ostream &os=cout);
int main ()
{
	ofstream outfile("2.2.txt", ios_base::app);
	vector<int> pent;
	const string title ("Pentagonal Numeric Series");

	if (calc_elements (pent, 0))
		display_elems(pent, title, outfile);

	if (calc_elements (pent, 8))
		display_elems(pent, title, outfile);


	if (calc_elements (pent, 14))
		display_elems(pent, title, outfile);

	if (calc_elements (pent, 138))
		display_elems(pent, title, outfile);
}

bool calc_elements (vector<int> &vec, int pos)
{
	if (pos <=0 || pos >64)
	{
		cerr << "sorry. Invalid position:" << pos << endl;
		return false;
	}
	for (int ix = vec.size()+1; ix <= pos; ++ix)
		vec.push_back( (ix*(3*ix-1))/2 );
	return true;
}
void display_elems (vector<int> &vec, const string &title, ostream &os)
{
	os <<'\n' << title << "\n\t";
	for (unsigned long  ix = 0; ix < vec.size(); ++ix)
		os << vec[ix] << ' ';
	os << endl;
}