Headers file doesn't see global variables - c++

Question

I have 2 two files called main.cpp and Volum_sumar.cpp. I included Volum_sumar.cpp in main.cpp header, but it doesn't see global variables in main.cpp
Can someone tell where is my mistake?
//main.cpp
#include <iostream>
#include <fstream>
#include <cstring>
#include <cmath>
#include <string>
#include <windows.h>
#include "Volum_sumar.cpp"
using namespace std;
fstream f("Figuri.txt");
fstream d("Dimens.txt");
int n=0;
struct Sfere
{
string codsf;
char culoare [15];
char material[15];
float xc,yc,r,arie,volum;
} sf[100],aux;
int main()
{
cazul3();
}
// Volum_sumar.cpp
#include <iostream>
#include <fstream>
#include <cstring>
#include <cmath>
#include <string>
#include <windows.h>
using namespace std;
void cazul3(){
double volt=0;
for(int i=0;i<n;i++)
{
volt=volt+sf[i].volum;
}
cout<<"VOLUMUL SFERELOR INREGISTRARE ESTE DE : "<<volt<<"cm3"<<endl;
}

Answer 1

You are going about this all wrong.
Like #CruzJean said, by including Volum_sumar.cpp directly in main.cpp, you are trying to access n and sf before they have even been defined.
#include'ing cpp files in other cpp files is bad practice. You should #include only header files. You are supposed to declare shared items in header files that cpp files can #include at needed, then compile your cpp files individually, and then finally link the resulting object files together to make the final executable file.
Global variables that need to be accessed across cpp files need to be instantiated in one cpp file and declared as extern in other files. The linker will resolve the extern references.
Try something more like this instead:
shared.h
#ifndef shared_h
#define shared_h
#include <string>
struct Sfere {
std::string codsf;
char culoare [15];
char material[15];
float xc, yc, r, arie, volum;
};
extern Sfere sf[100];
extern int n;
#endif
main.cpp
#include <fstream>
#include "shared.h"
#include "Volum_sumar.h"
std::fstream f("Figuri.txt");
std::fstream d("Dimens.txt");
int n = 0;
Sfere aux;
int main() {
cazul3();
}
Volum_sumar.h
#ifndef Volum_sumar_h
#define Volum_sumar_h
void cazul3();
#endif
Volum_sumar.cpp
#include <iostream>
#include "shared.h"
#include "Volum_sumar.h"
void cazul3() {
double volt = 0;
for(int i = 0;i < n; ++i) {
volt = volt + sf[i].volum;
}
std::cout << "VOLUMUL SFERELOR INREGISTRARE ESTE DE : " << volt << "cm3" << std::endl;
}