Question

explain the difference between #define and const

Answer 1

define is being precompiled and const is not and for better explanation just google it..

Answer 2

#define directive is a preprocessor directive; the preprocessor replaces those macros by their body before the compiler even sees it. Think of it as an automatic search and replace of your source code.

A const variable declaration declares an actual variable in the language, which you can use... well, like a real variable: take its address, pass it around, use cast it, convert it, etc.