/* File one.cpp */

#include "two.h"
#include <iostream>

int a = 0;

int main() {

test();
// Prints 22
std::cout << a << std::endl;
return 0;

}

/* File two.h */

void test(void);



/* File two.cpp */

// Says the a we use in this file is the same one as in one.cpp
extern int a;

void test(void) {
a = 22;
}