lines preceded with a hash sign(#). these are special lines of code that the Preprocessor resolves before running other lines. They can be:
- Header File imports like
#include <iostream> - C++ Macros
- C++ Conditional Compilation
Special properties
- You have NO semicolons after these.
- they are compiled TOP→BOTTOM. Scope does not matter
- They are file-local. Theyre discarded after compilation