Answers for "c++ header function definition"

what is a header in c++

// my_class.h
#ifndef MY_CLASS_H // include guard
#define MY_CLASS_H

namespace N
{
    class my_class
    {
    public:
        void do_something();
    };
}

#endif /* MY_CLASS_H */

how to declare a function in c++ header file

//somefile.h
#ifndef SOMEFILE_H
#define SOMEFILE_H
int add(int a, int b);
#endif