.h file help

This is going to sound stupid but... I forgot how to use .h files in basic c++ programs.

I know how to declare the .h file and use the functions, but I forgot how to make the function in the .h file.

Like what is the basic code for it?

main.cpp ->

Code:

---

#include "main.h"

int main()
{
        Hello();

        return 0;
}

---

main.h ->

Code:

---

#include <iostream>

void Hello()
{
        std::cout << "Hello World";
}

---

ahh yes void. Alright thanks a ton!

NO NO NO NO NO NO NO NO!

Headers should not contain non-template implentation.

Your headers should contain prototypes, type declartions, global consts, things like that.

foo.h

Code:

---

#ifndef FOO_H_
#define FOO_H_
// Header guards to prevent multiple includes in the same complation unit

struct FOO
{
  int x;
};

const unsigned int MAX_LENGTH = 20;

// The following function does foo
void foo(const FOO&);

#endif

---

foo.cpp

Code:

---

#include <iostream>
#include "foo.h"

void foo(const FOO& f)
{
  std::cout<<f.x<<std::endl;
}

---

main.cpp

Code:

---

#include <iostream>
#include "foo.h"

int main()
{
  FOO f = { 10 };
  foo(f);
}

---