C++ :: Global Variables For Multiple CPP Files

I am trying to get variables that are global to multiple files. I have mananged to make constant variables that are global but maybe not in the best way. In the header i have the constant variables being defined:

const int variable_Name = 5;

And the cpp file:

#include <iostream>
using namespace std;
#include "vars.h"
int main ( ) {
cout << variable_Name<< endl;
system ("pause");
return 0;
}

Is there a better way to do this and to make the variables able to be changed within the cpp files.