scope

Each symbol (variable or function) has a scope, which is the part of code within which it can be used.

global scope

can be used from anywhere in the program

file scope

can be used only within the file in which it is defined

block scope

can only be used in the block of code in which it is defined

Keyword static applied to a symbol defined outside any function in the current file gives the symbol file scope.

Keyword extern means the definition of the symbol is to be found outside this file (so compiler doesn't complain.)

Best practice: keep the scope of symbols as small as possible.

Note: scope is of a symbol independent of its type information. If you write code that uses a global function whose prototype has not been provided, the compiler may complain but build the program anyway.