including the libraries and defining some namespaces

header_files.cpp

#include <mlpack/core.hpp>
#include <mlpack/core/data/split_data.hpp>
#include <mlpack/methods/ann/layer/layer.hpp>
#include <mlpack/methods/ann/ffn.hpp>
#include <ensmallen.hpp>  /* The numerical optimization library that mlpack uses */ 

using namespace mlpack;
using namespace mlpack::ann;

// Namespace for the armadillo library(linear algebra library).
using namespace arma;
using namespace std;

// Namespace for ensmallen.
using namespace ens;