= Aula01

== Exercise 1

=== a)

Once the header is included, it checks if a unique value (usually something like HEADERFILE_H) is defined. Then if it's not defined, it defines it and continues to the rest of the page.

When the code is included again, the first ifndef fails, resulting in a blank file.

That prevents double declaration of any identifiers such as types, enums and static variables.

=== b)

All those function with `SllNode*` as their first argument, take a pointer to a `SllNode` as their first argument. This is a common pattern in C, where you pass a pointer to a struct to a function that will modify it.