#include <iostream>
#include <vector>

int main()
{
    std::cout << "Enter size of the array.\n> ";

    std::size_t dim;
    std::cin >> dim;

    std::vector<std::vector<double>> matrix(dim, std::vector<double>(dim));

    std::cout << "Enter the elements of the array.\n> ";
    for (std::size_t row = 0; row < dim; ++row)
        for (std::size_t col = 0; col < dim; ++col)
            std::cin >> matrix[row][col];

    std::cout << "The elements we're concerned with:\n";

    for (std::size_t row = 0; row < dim; ++row) {
        for (std::size_t col = 0; col < row; ++col)
            std::cout << matrix[row][col] << ' ';
        std::cout << '\n';
    }
}