Structures
Stack principle
wNOTE: Each of the big blocks is a struct (or
class) that has a pointer to another one.
Remember that the pointer only stores the memory location
of something, it is not that thing, so the arrow goes to
the next one. At the end, there is nothing for the pointer
to point to, so it does not point to anything, it should be set
to "NULL" to prevent it from accidentally pointing to a totally arbitrary and random location in memory (which is very bad).
