How can i use variables from a header file C++

Question

i've a header where i difined a variable for example an int n ; and i want to use this variable in source code for exemple in my header file n take a value 3 i want to conserve this value when including header file .
file.h
Int n=3;
file.cpp
int main(){
Cout<<n;
return 0;}
How to make that print 3
do you understand me 😅😅

Answer 1

Thank you Martin Taylor

Answer 2

it works with simple data but arrays the problem still present