pretty print

#include <iostream>
#include <string>
#include <cmath>

class PQ {
    int* heap;
    int num_items;
    bool has_children(int i) {
        return 2 * i + 1 <= num_items;
    }
    void write_pretty_print_lines(std::string* lines, int start_line, int end_line, int i) {
        if (i > num_items) {
            return;
        }
        int n_print_line = (end_line - start_line + 1) / 2 + start_line;
        std::string& curr_line = lines[n_print_line];
        curr_line += std::to_string(heap[i]);
        if (has_children(i)) {
            curr_line += " ";
            int digits = (heap[i] < 1 ? 1 : log10(heap[i]) + 1);
            curr_line += std::string(4 - digits, '-');
            curr_line += "+";
            int l_print_line = (end_line - start_line + 1) / 4 + start_line;
            int r_print_line = (end_line - start_line + 1) / 4 * 3 + start_line;
            for (int i = start_line; i < l_print_line; ++i) {
                lines[i] += "     ";
            }
            lines[l_print_line] += "    ";
            for (int i = l_print_line + 1; i < n_print_line; ++i) {
                lines[i] += "    |";
            }
            for (int i = n_print_line + 1; i < r_print_line; ++i) {
                lines[i] += "    |";
            }
            lines[r_print_line] += "    ";
            for (int i = r_print_line + 1; i <= end_line; ++i) {
                lines[i] += "     ";
            }
            write_pretty_print_lines(lines, start_line, n_print_line, 2 * i);
            write_pretty_print_lines(lines, n_print_line, end_line, 2 * i + 1);
        }
    }
    void bottomup_heapify(int i) {
        //starts at node closer to bottom, moves it upward until heap condition satisfied for that node
        while (i > 1 && heap[i] > heap[i / 2]) {
            std::swap(heap[i], heap[i / 2]);
            i /= 2;
        }
    }
    void topdown_heapify(int i) {
        //starts at node closer to top, moves down
        while (2 * i < num_items) {
            int j = 2 * i;
            if (j < num_items && heap[j] < heap[j + 1])
                ++j;
            if (heap[i] > heap[j])
                break;
            std::swap(heap[i], heap[j]);
            i = j;
        }
    }
    void print_item_array() {
        for (int i = 0; i <= num_items; ++i) {
            std::cout << heap[i];
            if (i != num_items)
                std::cout << " | ";
        }
        std::cout << std::endl;
    }
public:
    PQ(int* i, int n) {
        num_items = n;
        heap = new int[num_items + 1];
        heap[0] = 0;
        for (int j = 0; j != num_items; ++j)
            heap[j + 1] = i[j];
        //starting with last parent of a child
        for (int i = num_items / 2; i != 0; --i)
            topdown_heapify(i);
    }
    ~PQ() {
        delete heap;
    }
    std::ostream& pretty_print(std::ostream& out) {
        int full_tree_num_scores = pow(2, ceil(log(num_items) / log(2)));
        int num_lines = full_tree_num_scores * 2;
        std::string* lines = new std::string[num_lines];
        for (int i = 0; i != num_lines; ++i)
            if (i != num_lines / 2)
                lines[i] = " ";
        write_pretty_print_lines(lines, 0, num_lines - 1, 1);
        for (int i = 0; i != num_lines; ++i)
            out << lines[i] << std::endl;
        delete[] lines;
        return out;
    }
    void insert(int item) {

    }
};

int main()
{
    int items[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14};
    PQ pq(items, 15);
    pq.pretty_print(std::cout);
    return 0;
}