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I'm trying to understand the difference between variable definition, variable declaration, function definition, and function declaration. For example, site A would say that: int var=10; /* declare and initialize */ while site B would say: int y=20; /* global variable definition and initialization */ One is called a declarative and the other is called a definition. Why? Which one is the right one? And does initializing the variables make it a declaration or definition? Same thing with functions. There seems to be different rules for both functions vs variables and it's confusing me big time.

notevention
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  • A simple search result contains acceptable answers to your question: https://www.google.com/search?q=c+function+declarations+vs+definition – jwdonahue Sep 16 '20 at 17:55
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    Does this answer your question? [What is the difference between a definition and a declaration?](https://stackoverflow.com/questions/1410563/what-is-the-difference-between-a-definition-and-a-declaration) –  Sep 16 '20 at 17:55
  • Welcome to stack overflow. You should search for your problem before you ask. Otherwise your question will be flagged as duplicate. –  Sep 16 '20 at 17:57
  • Just one final thing that needs to be answered I'm confused about. If I used an identifier like int x = 10, would that automatically make it declared or defined? – notevention Sep 16 '20 at 17:57
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    An important point to understand, which is not always brought out, is that declarations and definitions are not disjoint. In fact, every object or function definition expressed in C source code is also a declaration of the object or function it defines. And particularly relevant to this question, every object declaration that initializes the declared object *is* a definition of that object. – John Bollinger Sep 16 '20 at 18:01
  • and there is the tentative definition which is only a declaration if followef by an explicit definition... – Antti Haapala Sep 16 '20 at 21:24

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