a pointer is (Savitch, p.698):
"the memory address of a variable"

*   it is a special kind of value

*   in C++, part of a pointer's type is not JUST that
    it's a pointer -- it is a pointer TO some type;

*   so -- in C++ -- how can I declare something
    to be of this special pointer type?
    ...and how can I then use it?

double *num_ptr;  // num_ptr's type is pointer to a
                  //    double
                  // num_ptr can now contain the
		  //    address of a double variable/
                  //    value somewhere in memory;

int *quant_ptr;   // quant_ptr's type is pointer to
                  //    an int
                  // quant_ptr can now contain 
                  //    the address of an int somewhere
                  //    in memory

boa *boa_ptr;     // boa_ptr's type is pointer to
                  //   a boa
                  // boa_ptr can now contain the
                  //    address of a boa instance
                  //    somewhere in memory

*   If I want to indicate that currently,
    a pointer is pointing to nothing,
    by STRONG convention you should set it to
    NULL

    *   (NULL is a named constant set in 
        the cstdlib)

boa_ptr = NULL;
num_ptr = NULL;
quant_ptr = NULL;

* [this is now a class coding standard --
  pointers that aren't currently pointing
  anywhere should be set to NULL]

*   But, we probably want our pointers to actually
    contain addresses at some point (to actually
    point TO something) --

ONE (of several) ways:

*   & can be a PREFIX operator,
    and when it is, it gets you the ADDRESS
    of the variable/lvalue it is in front of;

double my_salary;

// I can make num_ptr contain the address of
//    my_salary -- make it POINT TO my_salary --
//    with the statement:

num_ptr = &my_salary; // num_ptr now contains the
                      //   memory address -- the 
                      //   location in memory --
                      //   of value my_salary

int num_widgets;

quant_ptr = &num_widgets; // quant_ptr now contains
                           //    the memory address of
                           //    num_widgets

*   if you have a pointer to something --
    you are able to access the value WHERE
    that pointer is pointing --

    that is, you are able to access the value
    at the address;

    *   you use the prefix operator *
        to do this;

if I now say
cout << *quant_ptr << endl;

...this will print the int at the address in
   quant_ptr;
   or, if you prefer, it will print the int
   quant_ptr is pointing to;
   here, then, it will print the value of num_widgets

*  see ptr_play1.cpp to see the beginning of
   a working pointer example;