Makefile/main.cc

#include <iostream>

extern "C" {
#include "lib.h"
}

int main(int argc, char const *argv[]) {
  int x, y, sum;

  x = 15;
  y = 8;
  sum = calc_num(x, y);

  std::cout << "Sum: " << sum << std::endl;

  return 0;
}