Правильно связать модули

//main.cpp
#include <iostream>
#include "header.hpp"
using namespace std;
 
int main()
{
  f();
  system("pause");
}

//secondary.cpp
void f()
{
cout<<"f"<<endl;
}

//header.hpp
#include "secondary.cpp"
void f();

#include <iostream>
using namespace std;
 
void f()
{
    cout<<"f"<<endl;
}

#include "secondary.cpp"
#include <iostream>
using namespace std;
void f();

//main.cpp
#include "secondary.h"
#include "another.h"
using namespace std;
 
int main()
{
  f();
g();
  system("pause");
}

//secondary.cpp
#include "secondary.h"
void f()
{
cout<<"f"<<endl;
}

//secondary.h   - прадедушка всего
#include <iostream>
void f();

//another.cpp
#include "another.h"
void g()
{
cout<<"g"<<endl;
}

//another.h
#include "secondary.h"
void g();

//main.cpp
#include <iostream>
#include "header.hpp"
using namespace std;
 
int main()
{
  f();
  system("pause");
}

//secondary.cpp
void f()
{
cout<<"f"<<endl;
}

//header.hpp
#ifndef HEADER
#define HEADER
 
#include "secondary.cpp"
void f();
 
#endif

//! @file Point.h
#pragma once
 
class Point {
public:
  void draw() const;
};

//! @file Point.cpp
#include "Point.h"
 
void Point::draw() const
{
  // Implementation
}