Declaring and Defining Variables and Functions in Separate Files

Question

I'm confused about how to define and declare my variables and functions across multiple files WITHOUT resorting to global variables. Let's say I wanted to have separate header and source files declaring and defining variables and functions outside of 'main.cpp', to be used in 'main.cpp'.

EDIT: Apologies for my unclear example, but there will only ever be one balloon. I don't want balloon to be an object. It's just to hold some variables and functions.

//balloon.h
bool inflated = true;
void pop();

-

//balloon.cpp
#include "balloon.h"
void pop()
{
    inflated = false;
}

-

//main.cpp
#include "balloon.h"
int main()
{
    pop();
    return 0;
}

If I do this it gives me errors for having multiple definitions of 'inflated', and that it was first declared in 'balloon.cpp'.

If I use 'extern', it works, but gives me warnings about initializing and declaring 'inflated' in 'balloon.h'.

If I decide not to define inflated in balloon.h, it gives me errors about an undefined reference to 'inflated'.

What is the standard way of going about this? Am I missing some key information of variable/function declaration/definition across multiple files?

Answer 1

Straight away it should be

//balloon.h
extern bool inflated;
void pop();

---

//balloon.cpp
#include "balloon.h"

bool inflated = true;

void pop() {
    inflated = false;
}