Pointers and References:
In C++ (and C) we distinguish:
rvalues = the sorts of things that can go on the RHS (right-hand side) of
assignment operator.
lvalues = the sorts of things that can go on the LHS of an assignment operator.
Since the purpose of an assignment operator is to change a location in memory, the
only things that can go on the LHS are things that in some way translate into the
address of a location in memory.
This is why "X = 2" is OK (because X is an lvalue),
but "2 = X" is not OK, because 2 is an rvalue, not an lvalue.
Pointers are addresses treated as rvalues, so you put them into other variables.
int x = 17;
int * xp; // declares a pointer variable, i.e., it can hold an address.
xp = &x; // puts the address of x into xp
Why use pointers?
(1) Pointers often represent relationships between objects. For example, in an
organization chart, the links (or edges) show who each person's supervisor is. If we
were to do this in OOP, the natural way to do it would be to have a pointer from the
object representing an employee to the object representing their supervisor.
Then we can go directly from the employee to their supervisor.
