How do you define a "Hello World" function in a seperate file in c-CodePudding

and I apologize for asking a very basic question, but basically, I'm not able to wrap my head around include "fileImade.h"

I'm trying to write a main function, that's something like

int main()
{
int x = 5;
int y x 6;
std::cout << add(x, y) << std::endl;
}

where add() is defined in a separate .cpp file, and #include -ed in this one, (I'm doing this because I'm getting the point where my code is getting impractically large to do in a single file.), but my understanding is that you need a header file to... Glue your other files together, or I guess mortar them if the files are the bricks, but I absolutely cannot figure out how to make this work for the life of me.

(while using g ), should I tag -I? According to me googling, yes, according to my compiler output, no.

Should I write a header file and a .cpp files for the add() function? Apparantly, yes, or no, if I choose to write both files in the command line before the -o.

Should I include a forward declaration of the function in my main.cpp file? Again, according to the internet, yes, though that's not working terribly well for me.

So to my question: Can someone show me a main() function that calls a hello world() function in a separate file?

I'm honestly at my wits' end with this because all the guides seem to be on defining classes in header files, which, while useful, is a bit beyond the scope of what I'm attempting right now.

Thank you in advance for reading, and any advice offered.

CodePudding user response：

The logic of the file separation may be imagined as:

(single file program)

/// DECLARATION of all functions needed in the main
int add(int x, int y); // declaration of add

///
int main()
{
    std::cout << add(2, 3) << std::endl;
    return 0;
}

/// IMPLEMENTATION of all functions needed in the main
int add(int x, int y)
{
    return x   y;
}

The next you have to do is move all declarations to the headers and implementations to the cpps:

(separated files program)

/// add.h
#ifndef ADD_H /// https://en.wikipedia.org/wiki/Include_guard
#define ADD_H
int add(int x, int y);
#endif

/// main.cpp
#include "add.h"

int main()
{
    std::cout << add(2, 3) << std::endl;
    return 0;
}

/// add.cpp
#include "add.h"

int add(int x, int y)
{
    return x   y;
}