Preprocessor directives in C

[Qomplainerz]

Preprocessor directives are instructions to the compiler before actual compilation.
// #define directive for a macro
#define PI 3.14159

// #include directive to include a header file
#include <stdio.h>

// Other preprocessor directives
#ifdef DEBUG
    printf("Debug mode\n");
#else
    printf("Release mode\n");
#endif