Programming

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Programming Scratch
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Programming

• Learning to program is ultimately about learning
  to think logically and to approach problems
  methodically.
• The building blocks out of which a programmer
  constructs solutions, meanwhile, are relatively
  simply.

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Problem-Solving and Project-Design Skills

• logical reasoning
• breaking complex problems into simpler parts
• debugging problems
• developing ideas from initial conception to
  completed project
• sustained focus and perseverence

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Fundamental Ideas about Computers and Programming

• computer programs tell the computer precisely
  what to do, step-by-step
• writing computer programs doesnt require special
  expertise, just clear and careful thinking

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Programming

• Common in programming, for instance, are "loops"
  (whereby a program does something multiple times)
  and "conditions" (whereby a program only does
  something under certain circumstances. Also
  common are "variables" (so that a program, like a
  mathematician, can remember certain values).

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Statements

• In programming, a statement is simply a directive
  that tells the computer to do something. Think of
  it as a command or an instruction. In Scratch,
  any block whose label reads like a command is a
  statement.

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Statements

• One such block instructs a sprite to say
  something

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Statements

• Another such block instructs a sprite to go to
  some location

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Sequence

• To create a program in Scratch, you need to think
  systematically about the order of steps

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Boolean Expression.

• In programming, a Boolean expression is an
  expression that is either true or false. In
  Scratch, any block shaped like an elongated
  diamond is a Boolean expression.
• One such block is

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Boolean Expression.

• Another such block is
• After all, it is either true that some number is
  less than another number or it is false.

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Boolean Logic

• and, or, or not are examples of boolean logic.

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Conditions

• In programming, a condition is something that
  must be true in order for something to happen. A
  condition is thus said to "evaluate to true" or
  "evaluate to false." In Scratch, any block whose
  label says "if," "when," or "until" is a sort of
  conditional construct.

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Conditions

• One such block is

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Conditions

• The previous construct is generally known as an
  "if construct." With it can we instruct a sprite
  to say hello only if, say, the user has depressed
  the mouse button

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Conditions

• A related construct is the "if-else construct"

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Conditions

• With the previous construct can we instruct a
  sprite to say hello or goodbye, depending on
  whether the user has depressed the mouse button

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Conditions

• Realise that these constructs can be nested to
  allow, for example, for three different
  conditions. This construct could be called an
  "if-else if-else construct".

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Conditions

• Another conditional block is
• Yet another such block is

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Conditional Statements

• if, forever-if, if-else repeat-until and
  waituntil check for a condition

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Loops

• Sometimes, you want one or more statements to be
  executed multiple times in a row. To implement
  this behavior, we turn our attention to loops.

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Loops

• In programming, a loop can induce multiple
  executions of statements. In Scratch, any block
  whose label begins with "forever" or "repeat" is
  a looping construct.

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Loops

• One such block is
• This construct allows us, for instance, to
  instruct a sprite to meow every other second

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Loops

• Another block allows you to loop a specific
  number of times
• And another block allows you to loop until some
  condition is true

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Iteration (Looping)

• forever and repeat can be used for iteration
  (repeating a series of instructions)

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Variables

• Sometimes, you want execute some statement
  multiple times, each time varying your behavior
  ever so slightly. We thus turn our attention to
  variables.

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Variables

• In programming, a variable is a placeholder for
  some value.
• Variables allow us, for instance, to instruct a
  sprite to count up from 1

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Variables

• A variable that only takes on a value of true
  (i.e., 1) or false (i.e., 0), incidentally, is
  called a Boolean variable.

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Variables

• The Variables category allows you to create a new
  variable and use it in a program.

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Threads

• In programming, a thread is like a mini-program
  within a program that can execute at the same
  time as other threads.
• One such block is

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Threads

• It's often helpful to use separate threads for
  conceptually distinct tasks. For instance, you
  might want to keep track of whether the user ever
  presses some key during a program's execution in
  order to, say, toggle sound on and off

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Threads
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Threads

• Notice how, in the above, the left-hand thread
  handles meowing, if appropriate, whereas the
  right-hand thread constantly checks and remembers
  whether the user has muted or unmuted sound by
  pressing space'.

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Threads (Parallel Execution)

• Launching two stacks at the same time creates two
  independent threads that execute in parallel.

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Events

• In programming, multiple threads can communicate
  with each other by signaling events and handling
  events. An event, then, is like a message from
  one thread to another.
• A block that signals an event is

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Events

• A block that handles an event is

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Events

• Not only can events be signaled by blocks, they
  can also be signaled by a user's actions.
  Clicking Scratch's green flag, for instance,
  effectively signals an event that is handled by

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Events

• In Scratch, not only do events enable threads to
  communicate, they also allow sprites to
  communicate with each other.

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Event Handling

• when key pressed and when sprite clicked are
  examples of event handling responding to events
  triggered by the user or another part of the
  program

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Synchronisation

• broadcast can coordinate the actions of multiple
  sprites.
• For example, Sprite1 sends the message winner
  when condition is met

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Synchronisation

• This script in Sprite2 is triggered when the
  message is received

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Real-Time Interaction

• mouse_x, mouse_y, and loudness can be used as
  dynamic input for real-time interaction

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Time Triggering

• Scratch includes an internal clock that you can
  access with timer.

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Random Numbers

• The pick random block selects random integers
  within a given range.

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Object-Oriented Programming

• Each sprite can have its own scripts and data.

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User Interface Design

• You can design interactive user interfaces in
  Scratch for example, using clickable sprites to
  create buttons.

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Data Types

• Different data types (such as numbers and
  booleans) are represented by different shapes in
  Scratch