For Dummies Beginning Programming with C++ 978-0-470-61797-7 사용자 설명서
제품 코드
978-0-470-61797-7
10
Part I: Let’s Get Started
For example, I say things to my son like, “Wash the dishes” (for all the good it
does me). This seems like clear enough instructions, but the vast majority of
the information contained in that sentence is implied and unspoken.
does me). This seems like clear enough instructions, but the vast majority of
the information contained in that sentence is implied and unspoken.
Let’s assume that my son knows what dishes are and that dirty dishes are nor-
mally in the sink. But what about knives and forks? After all, I only said dishes,
I didn’t say anything about eating utensils, and don’t even get me started on
glassware. And did I mean wash them manually, or is it okay to load them up
into the dishwasher to be washed, rinsed, and dried automatically?
mally in the sink. But what about knives and forks? After all, I only said dishes,
I didn’t say anything about eating utensils, and don’t even get me started on
glassware. And did I mean wash them manually, or is it okay to load them up
into the dishwasher to be washed, rinsed, and dried automatically?
But the fact is, “Wash the dishes” is sufficient instruction for my son. He
can decompose that sentence and combine it with information that we both
share, including an extensive working knowledge of dirty dishes, to come up
with a meaningful understanding of what I want him to do — whether he does
it or not is a different story. I would guess that he can perform all the mental
gymnastics necessary to understand that sentence in about the same amount
of time that it takes me to say it — about 1 to 2 seconds.
can decompose that sentence and combine it with information that we both
share, including an extensive working knowledge of dirty dishes, to come up
with a meaningful understanding of what I want him to do — whether he does
it or not is a different story. I would guess that he can perform all the mental
gymnastics necessary to understand that sentence in about the same amount
of time that it takes me to say it — about 1 to 2 seconds.
A computer can’t make heads or tails out of something as vague as “wash the
dishes.” You have to tell the computer exactly what to do with each different
type of dish, how to wash a fork, versus a spoon, versus a cup. When does
the program stop washing a dish (that is, how does it know when a dish is
clean)? When does it stop washing (that is, how does it know when it’s
finished)?
dishes.” You have to tell the computer exactly what to do with each different
type of dish, how to wash a fork, versus a spoon, versus a cup. When does
the program stop washing a dish (that is, how does it know when a dish is
clean)? When does it stop washing (that is, how does it know when it’s
finished)?
My son has gobs of memory — it isn’t clear exactly how much memory a
normal human has, but it’s boat loads. Unfortunately, human memory is
fuzzy. For example, witnesses to crimes are notoriously bad at recalling
details even a short time after the event. Two witnesses to the same event
often disagree radically on what transpired.
normal human has, but it’s boat loads. Unfortunately, human memory is
fuzzy. For example, witnesses to crimes are notoriously bad at recalling
details even a short time after the event. Two witnesses to the same event
often disagree radically on what transpired.
Computers also have gobs of memory, and that’s very good. Once stored, a
computer can retrieve a fact as often as you like without change. As expen-
sive as memory was back in the early 1980s, the original IBM PC had only
16K (that’s 16 thousand bytes). This could be expanded to a whopping 64K.
Compare this with the 1GB to 3GB of main storage available in most comput-
ers today (1GB is one billion bytes).
computer can retrieve a fact as often as you like without change. As expen-
sive as memory was back in the early 1980s, the original IBM PC had only
16K (that’s 16 thousand bytes). This could be expanded to a whopping 64K.
Compare this with the 1GB to 3GB of main storage available in most comput-
ers today (1GB is one billion bytes).
As expensive as memory was, however, the IBM PC included extra memory
chips and decoding hardware to detect a memory failure. If a memory chip
went bad, this circuitry was sure to find it and report it before the program
went haywire. This so-called Parity Memory was no longer offered after only
a few years, and as far as I know, it is unavailable today except in specific
applications where extreme reliability is required — because the memory
boards almost never fail.
chips and decoding hardware to detect a memory failure. If a memory chip
went bad, this circuitry was sure to find it and report it before the program
went haywire. This so-called Parity Memory was no longer offered after only
a few years, and as far as I know, it is unavailable today except in specific
applications where extreme reliability is required — because the memory
boards almost never fail.
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