C++ preprocessor directives

[SlayerApocalypse666]

Hi guys, i've been scratching my head about these for a while now, i'm not sure WHAT and WHY they should be used for.

They are statement that are processed before the compilation is done, *as i've read*. But ... why would you use instead of just using a regular variable in your program ?? Anybody has any idea.

#define ZERO 0;
#define TRUE 1;

instead of

int ZERO{}; or int ZERO = 0; or int ZERO = {0}; or int ZERO = {};
int TRUE{1};

i just don't get it guys. Plus why does #define doesnt require a type for the variable.....? i'm really confused about em.

Thx alot.