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PROFESSOR ERIC GRIMSON: As I've
done in the previous lectures,
00:00:23
let me set the stage for what
we've been doing, so we can
00:00:26
use that to talk about what
we're going to do today.
00:00:30
So far, we have the
following in our language.
00:00:35
Right, we have assignment.
00:00:41
We have conditionals.
00:00:46
We have input/output.
00:00:47
And we have looping constructs.
00:00:55
These are things like
FOR and WHILE loops.
00:01:00
And of course we've got
some data to go with that.
00:01:04
One of the things we said last
time was, with that set of
00:01:07
things, the ability to give
values-- sorry, to give names
00:01:11
to values-- the ability to make
decisions, the ability to loop
00:01:14
as a function of that, the
ability get things in and out,
00:01:17
we said that that actually gave
us a language we said
00:01:21
was Turing-complete.
00:01:26
And that meant, in English,
that this was enough
00:01:29
to write any program.
00:01:32
Now that's a slight lie-- or
actually in these days of
00:01:34
political debates, a slight
misspeaking, a wonderful word--
00:01:39
it is technically correct.
00:01:40
It is enough to allow us to
write any program, but it's
00:01:43
not enough to allow us to
easily write any program.
00:01:47
And so I joked, badly, I'll
agree, at the end of last
00:01:50
lecture, that we can just stop
now, go straight to the final
00:01:52
exam, because this is
all you need to know.
00:01:54
The point is, yes it's enough
to start with, but we want to
00:01:58
add things to this that let
us problem solve well.
00:02:00
And one of the things to think
about is, even though I've got
00:02:03
all of that, let's think about
what I could do, if I wanted
00:02:06
to write a piece of code.
00:02:09
Right now, you've got to
write it in one file.
00:02:11
It's a long sequence of
instructions, it starts at the
00:02:14
beginning, walks through, may
jump around a little bit, but
00:02:17
eventually comes
down at the end.
00:02:19
It's okay for the things
you're doing for the
00:02:21
early problem sets.
00:02:23
Ten lines of code.
00:02:24
Twenty lines of code.
00:02:25
Imagine instead, you're writing
code that's a hundred thousand
00:02:28
lines, a million
lines, of code.
00:02:31
You don't want to write
it in this form.
00:02:34
All right, and the reason
you don't want to do
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