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A declaration is a form of statement, which expresses (or declares) some idea; declarations attempt to argue that something is true. Some types of written text are said to be declarations, such as the US Declaration of Independence.

Computer Science

In computer science, a declaration specifies a variable's dimensions, identifier, type, and other aspects. The declaration, and any related initializer, forms the definition; usually, the declaration and definition are the same thing. Definitions reserve memory. Definitions and declarations can also be used for subroutines (functions); where, they are sometimes referred to as "prototypes". Once again, in some cases the definition and the prototype are the same thing.

Initialization allows a variable to be defined as "equal" to something. Below is an example of a C++ function which declares an integer variable, x; this is followed by an example where the variable has been initialized to equal seven, x = 7:

void example1()
 int x;

void example2()
 int x = 7;