Preprocessor Directives

The preprocessor runs before compilation and handles macros, file inclusion, and conditional compilation.

#define PI 3.14159
#define SQUARE(x) ((x)*(x))

#if defined(_WIN32)
    #define PLATFORM "Windows"
#else
    #define PLATFORM "Other"
#endif

Common directives:

• #include "file.h" – include header.
• #define / #undef – macros.
• #if, #ifdef, #ifndef, #else, #elif, #endif – conditional compilation.
• #pragma – implementation‑specific instructions.

Macros are textual replacements; they are not type‑checked. Use static inline functions for safer alternatives when possible.