Transcript Unit 2 - School of Computer Science

Introduction to Programming
G50PRO
University of Nottingham
Unit 2 : Introduction To Scratch
Paul Tennent
http://paultennent.wordpress.com/G50PRO.html
[email protected]
Room C41
What is Scratch?
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Scratch is a free programmable toolkit that enables
users to create games, animated stories, and
interactive art
Enables users to share programs over the Internet
Scratch is developed by the Lifelong Kindergarten
Group at the MIT Media Lab, with funding from the
National Science Foundation, Microsoft, Intel
Foundation, Nokia, and the MIT Media Lab research
consortia.
Getting Started With Scratch
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Open new project
Choose, create or edit your Sprite
Choose your background
Write your program
Programming In Scratch
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Click on the sprite you want to program, and select the
“Scripts” tab.
The Scripts area is where you “build” your program by using
the programming blocks.
In the upper, left-hand corner of your Scratch window, you will
see 8 buttons .
Each of these buttons have programming blocks in those
particular areas.
Programming In Scratch
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To program a sprite, drag blocks from the
Blocks Palette to the Scripts Area. To run a
block, click on it.
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Create scripts (programs) by snapping blocks
together into stacks. Click anywhere on the
stack to run the whole script, from top to
bottom
Scratch Stage
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The Scratch stage is 480 pixels wide and
360 pixels high.
180
240
-240
-180
Scratch Blocks
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Motion
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Animate sprites
Control and Sensing
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controls how many times an event happens, how long an
event happens, or when an event happens.
conditional statements (“if statements” or “if-else
statements”)
Write code so that if the user presses the Space key on the
keyboard, the sprite will move 20 steps and change
direction.
Scratch Blocks
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Sound
Looks
Pen
Operators
Variables
Starting From Scratch
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Scratch has all of the common elements used
in all programming languages.
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Conditional statements
Loops
Variables
Events
Branching
(Conditional Statements)
Make Tea
START
Is kettle
full?
yes
Boil Kettle
no
Fill kettle
Conditional Statements
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If [Boolean]
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Then
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Do this
Else
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Do the other
Comparisons
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==
<
>
<=
>=
!=
Equals
Less than
More than
Less than or equal to
Greater than or equal to
Not equal to
Loops
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Simplify the coding of repetitive tasks
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Giving the people in a company a 10% rise
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Employee 1 salary = 1.1*Employee 1 salary
Employee 2 salary = 1.1*Employee 2 salary
…
Employee 99 salary = 1.1*Employee 99 salary
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Loops
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Simplify the coding of repetitive tasks
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Giving the people in a company a 10% rise
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For i = 1 to 99
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Employee i salary = 1.1*Employee i salary
Loops
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There are a lot of different standard types of
loop
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Scratch only has some of them
Flow control
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Flow control
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In computer science flow control refers to the
order in which the statements or instructions are
executed or evaluated.
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Branches (Conditional Statements)
Loops
Variables
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a variable is a facility for storing data
One of the most powerful features of a
programming language is the ability to
manipulate variables.
A variable is a named location that stores a
value.
Values are things that can be printed, stored
or operated on. (numbers, letters, Strings,
etc.)
Variables
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each variable will have
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Name
Value
Location in memory
X = 100
Y = 20
Assignment statement
Declare str
str = “Hello”
the idea is straightforward:
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When you declare a variable, you create a named
storage location.
When you make an assignment to a variable, you
give it a value.
BankBalance
Payment
700
Check
Balance
700
700
Events
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You can’t run all of the elements of a program
at once
Things happen when the relevant event
triggers them
The main event in Scratch is the green flag
There are other custom events that you can
add
Summary
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Scratch Programming Blocks
Conditional Statements allow us to make
decisions about what to do next
Loops allow us to perform repetitive tasks
Variables record the values and state of
elements of a program
Events trigger different elements of the
program to be run at the correct time