unresolved external symbol "int randomNumber" [duplicate] - c++

Question

This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
When to use extern in C++
(4 answers)
Closed 8 years ago.
Can please someone explain me how to link the functions # functions.cpp to main.cpp
note: I want both files functions.cpp and main.cpp to use the same variables from header.h
Thank you!
main.cpp
#include "Header.h"
#include <iostream>
using namespace std;
int multi();
int printOutRanomdNumber();
int main()
{
cout << "Eneter a number you want to multiply" << endl;
cout << multi() <<endl;
cout << printOutRanomdNumber();
system("pause");
return 0;
}
header.h
#ifndef _HEADER_
#define _HEADER_
#include <iostream>
using namespace std;
extern int randomNumber;
int multi();
int printOutRanomdNumber();
#endif
functions.cpp
#include "Header.h"
#include <iostream>
using namespace std;
int multi()
{
int x;
cin >> x;
return(x=x*x);
}
int printOutRanomdNumber()
{
cout << "Please enter a random number" << endl;
cin >> randomNumber;
return (randomNumber);
}

Answer 1

The error is because you've not defined int randomNumber in any of your files.
You need to define randomNumber in one of the .cpp files, I'm guessing functions.cpp makes more sense here.
Also you can get rid of these lines in main.cpp since you're including Header.h which provides the prototypes already.
int multi();
int printOutRanomdNumber();