THINK++ — Engineering Visualized

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Preprocessor Directives

Instructions processed by the preprocessor BEFORE the actual compilation starts. They always begin with a hash # symbol.

#include

Inserts the contents of a header file into the current file.

#define

Creates a macro (text substitution) or constant.

#ifdef / #ifndef

Conditional compilation based on whether a macro is defined.

#pragma

Compiler-specific instructions (e.g., #pragma once).

NOTE ON SEMICOLONS

Preprocessor directives are NOT C++ statements. Do NOT put a semicolon ; at the end of them.

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