Is the following statement a declaration or definition?
extern int i;
Answer: A
Correct answer: Declaration
extern int i; announces that an object named i of type int exists somewhere, without reserving storage for it. A definition is what allocates the storage, and there must be exactly one of those in the program however many declarations refer to it.
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Suppose a program is divided into three files f1, f2 and f3, and a variable is defined in the file f1 but used in files f2 and f3. In such a case would we need the extern declaration for the variables in the files f2 and f3?
Answer: A
Correct answer: Yes
The definition lives in one file and reserves the storage; the other two files must be told that the name exists and what type it has, or the compiler has nothing to check their uses against. That is precisely what extern does, and the declaration is conventionally put in a header included by both.
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