BFOIT - Introduction to Computer Programming

# Pseudocode - Screencast Script

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Welcome to BFOIT's Introduction to Computer Programming website.

This is a short screencast overview of the third lesson:

Pseudocode.

In the first lesson you learned about the gap between us humans
and our native languages and a computer and it's native language.

In these lessons we are learning to program with Logo, a high-
level programming language; it is about as close as we can get to
the English language.  But the version of Logo we are using only
knows approximately one hundred and fifty words - much less than
you or I know.  And, it has some strange punctuation rules.  In
this lesson you will see how to use English to get you a step
closer to the Logo code you write.

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[ position to Summary ]

Pseudocode uses structural concepts of computer programming along
with a native language.

We are going to use pseudocode combined with an age-old method for
solving math problems - George Polya's steps which he outlines in
his book How to Solve It.  His steps are:

1. Understanding the Problem,

2. Devising a Plan,

3. Carrying Out the Plan, and

4. Looking Back.

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[ Bring up the Windows Paint program with an image of TG with a ]
[ BowTie loaded into the background                             ]

Let's work through an example. It has to be very simple to keep
this screencast short.  Let's get the turtle to draw a bowtie.

To understand the problem, what our Logo program will consist of,
I'll just sketch an example of a crude, artistic rendition of a
bowtie.

So, it looks like we need to get the turtle to draw two triangles,
each a sort-of reflection of the other.

I think we now understand what our program needs to do.  We've
completed the the first step of phase.

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Next I'll devise a plan; I'll describe what I'm going to do in
English, as Logo comments in TG's editor.

[ show bringing up the editor and type in the first few comments ]

[ ; BowTie                                                         ]

[ ; initialize: clear the canvas. make sure the turtle is at home, ]
[ ;             heading north, with a wide, yellow pen             ]

[ ; draw the triangle to the right of home, ending back at home    ]

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- show typing in the last line of pseudocode

[ ; hide the turtle ]

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So now it's time for carrying out the plan.

I'll convert the pseudocode to Logo instructions.

[ type in the first line of instructions ]

[ home clean setheading 0 setpencolor 6 setpensize 10 ]

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One great thing about Logo programming environments is that they
are highly interactive.  Since I do not know the angles and lengths
of the legs of the triangle I need, I'll just experiment

[ right 45 forward 150 home right 15 forward 200 forward 50 ]

[ right 90 right 30 forward 200 forward 20 home             ]

Now I can use the results of this experimentation to fill in the
remaining Logo instructions.

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[ With completed program in the Editor                ]

I've now completed the translation from pseudocode to Logo. Let's
see how it looks.

[ Choose the menu item: Window -> Editor -> Interpret ]

Looks pretty good to me.

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The Pseudocode lesson will walk you through writing a program that
draws the "collection of boxes" exercise from the previous lesson.

Go to it... and remember - HAVE FUN!

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