Definitions

Definitions and declarations look much the same in C; it can also be difficult to tell the difference between initialization and assignment because they use the same symbol. Here I am just trying to visually lay out the various types of statements in order to show clearly what their differences and relationships are.

C/C++

	Variable		Function
Type	Global	Local	(Global)
Declaration	extern int x;		extern int fn();
Definition	int x;		int fn() { ... }
Initialization	int x = 1;
Assignment		x = 1;

Note that in this table, "global" and "local" are used both for the type of variable and for the type of scope where the statement appears (if these are different, no code appears in the given cell). For example,

x = 1;

may be used to assign to a global variable inside a function, but such a statement may not appear in the global scope. Likewise, you may declare a global variable inside a function, but you cannot use the same syntax for a local variable at the local scope.

See also

• https://stackoverflow.com/questions/23345554/the-differences-between-initialize-define-declare-a-variable