Anyway, I just wanted to say that these tutorials are really good. Thanks. ;D

Typically, people use global variables for one of three reasons:
1) Because they don’t understand C++ variable passing mechanics, or they’re being lazy.
2) To hold data that needs to be used by the entire program (eg. configuration settings).
3) To pass data between code that doesn’t have a caller/callee relationship (eg. multi-threaded programs)

Obviously #1 isn’t a good reason at all. Once you get into C++ classes, there are better ways to do #2 (eg. static classes). That pretty much leaves #3, and maybe a few other cases I’m not aware of.

Basically, the only time you should use a global variable is if there is no practical way to do what you want using local variables and variable passing mechanics. In my opinion, use of globals should always be a last resort — so in a way, it’s a “you’ll know it when you run into it” situation, as there simply won’t be any other reasonable way to proceed.

I was facing problem with global variable declaration and using it into mutiple files.

The problem is fixed.