Header file and extern keyword

Question

I am having a lot of issue using extern variable and header files. I have read through sections of books and searched the web for hours but I haven\'t been able to figure out. A

Answer 1

An external variable must be defined, exactly once, outside of any function; this sets aside storage for it. The variable must also be declared in each function that wants to access it;

check this link. well explained How do I use extern to share variables between source files?