Question

How can I create bunch of methods that doesn’t depend on any object ( in my file there is no classes , no objects , no main , nothing but the methods) all in one cpp/hpp file and how to declare them ?

Answer 1

If you want them to be public, i.e. available in multiple translation units, the best way is to include them in a namespace, declare them in the header and implement them in a single implementation file:

//functions.h

namespace MyFunctions
{
   void foo();
   void goo();
}

//functions.cpp

namespace MyFunctions
{
   void foo() {}
   void goo() {}
}

IMPORTANT

If you provide the definition in the header, you should mark them inline, otherwise including that header in multiple translation units might result in a linker error:

//functions.h
inline void foo() {  
    //..
}
inline void goo() { 
    //..
}

If you only want them available in a translation unit, define them in that implementation file in an anonymous namespace (or declare them static):

//fileThatUsesFunctions.cpp

namespace
{
    void foo() {}
    void goo() {}
}