THINK++ — Engineering Visualized

Structure

Declaration vs Definition

In C++, a function must be known to the compiler before it's called. This is handled by splitting it into declaration (prototype) and definition.

DECLARATION (PROTOTYPE)

int add(int a, int b);

Tells the compiler about the function name, return type, and parameters. Usually goes above main() or in a header file.

DEFINITION (BODY)

int add(int a, int b) {
    return a + b;
}

The actual implementation of the function logic.

WHY DECLARE?

Declarations allow functions to be defined in any order and enable cross-file function calls. It's the "contract" the compiler uses to verify function calls.

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Function Declaration Definition

Function Declaration Definition

Declaration vs Definition

Declaration vs Definition