C++ 11.03.2022 BST

#include <iostream>
#include <cmath>
void PREORDER(int tablica[], int size, int a = 1) {
    if (a-1 < size) {
        if(tablica[a - 1]!=0)
            std::cout << tablica[a-1] << " ";
        PREORDER(tablica,size, 2 * a);
        PREORDER( tablica, size, 2 * a+1);
    }
}
void INORDER(int tablica[], int size, int a = 1) {
    if (a - 1 < size) {
        INORDER(tablica, size, 2 * a);
        if (tablica[a - 1] != 0)
            std::cout << tablica[a - 1] << " ";
        INORDER(tablica, size, 2 * a+1);
    }
}
void POSTORDER(int tablica[], int size, int a = 1) {
    if (a - 1 < size) {
        POSTORDER(tablica, size, 2 * a);
        POSTORDER(tablica, size, 2 * a+1);
        if (tablica[a - 1] != 0)
            std::cout << tablica[a - 1] << " ";
    }
}
int main()
{
    int tablica[] = { 20, 16, 28, 12, 18, 0, 30, 5, 14, 0, 19, 0, 0, 0, 0, 0, 0, 13, 15, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
    PREORDER(tablica, 31);
    std::cout << std::endl;
    INORDER(tablica, 31);
    std::cout << std::endl;
    POSTORDER(tablica, 31);
    std::cout << std::endl;
}