INTRODUCTION


our own C/65, are "loose" enough to allow you to cheat most of the
time.)
     Here, the declarations establish that "pc" (program counter) will
always point to (i.e., contain the address of) a byte-sized item. But "pi"
will always point to a word-sized (double byte) item. Now, actually,
these variables point to nothing until we put an address into them,
which we proceed to do via "pc = 84" and "pi = 85".
     And, finally, the actual "assignments" to or from memory are
handled by the last line in each problem solution. Now, all this looks
very complicated and hardly worthwhile, but the advantage of C is,
once we have made all our declarations, that we can use the variables
and structures wherever we need them in a program module, secure in
the knowledge that our code is at least partially self-documented.

Pascal
Actually, standard Pascal has no methods whatsoever available to
solve these problems. Remember, Pascal is a "school" language, and
access to the machine level was definitely not a desirable feature in
such an environment. In fact, most of the Pascal compilers in use today
have invented some way to circumvent the restrictions of "standard"
Pascal, and it is largely because of such "inventions" that the various
versions of the language are incompatible.
     Anyway, Atari Pascal does provide a method to access individual
memory cells. I am not sure that the method I will show here is the best
or easiest way, but it appears to work. Again, the solution is presented
first:

     Note: the code in this first part is common to both problems, both
        for H and V.
        (* in the "type" declarations section *)
        charaddr = record
           row : char;
           end;
        wordaddr = record
           col : integer;
           end;
        (* in the "var" declarations section *)
        pc : ^charaddr;
        pw : ^wordaddr;
        rowcrs : absolute [84] ^charaddr;
        colcrs : absolute [85] ^wordaddr;

     Problem 1.
        (includes the above common code)
        (* execution code in the procedure *)
        pc : = rowcrs;
        pw : = colcrs;