Scope
Definition​
Each time we declare a variable, depending on where it is declared, we assign it to a certain scope.
A scope is a region of the program (a code block) where the name of that variable can be used to refer to the entity. In other words, it is the extent of the program code within which the variable can be accessed or declared or worked with.
In fact, each name that appears in a C++ program is only visible in some limited portion of the source code called its scope, also known as visibility.
Types of scope​
There are mainly two types of variable scopes:
Local (block scope)​
Local variables are variables declared inside a code block (so anything between { and },
like in functions, if statements, loops etc.)
and they do not exist outside the block in which they are declared, i.e. they can not be accessed
or used outside that block. Local variables are not known to the functions outside their own.
I know that we still haven't talked about functions and constructs, but don't worry if you don't
understand this now. You can come back here for reference after reading those parts or when you
encounter the error Error: X was not declared in this scope. I think, though, it's important to
introduce and cover this topic before moving on.
Global (file scope)​
Global variables are defined outside of all the functions or blocks, usually on top of the program after the linking section. They are visible and accessible everywhere in the program, unlike local variables, meaning that they are available for use throughout your entire program after their declaration.
For now, we don't need to know how to declare global variables. Just make sure to know the difference between these two scope types.
Naming conflicts​
It's usually best practice to avoid global variables when unnecessary because it's easy to generate conflicts.
What if we have two variables with the same name but different scopes?
Usually when two variables with the same name are defined then the compiler produces a compile-time error. But if the variables are defined in different scopes then the compiler allows it. Whenever there is a local variable defined with the same name as that of a global variable then the compiler will give precedence to the local variable1.