You already know how to make things happen in Scratch: sequences, variables, loops, decisions, and fixing bugs. Today the question is different. How do you turn a fuzzy idea into a plan you can actually build?
You will meet four steps coders use to break a problem down, use them on a build you choose, and start that build in Scratch.
Coders use four steps of computational thinking to turn a big idea into something they can build. Meet each step on a worked example as you go.
Idea: a simple chase where your sprite catches another sprite and the score goes up.
- Decomposition (smaller pieces): your sprite moves; the target moves; detect a touch; score changes.
- Pattern recognition (what repeats or what you already know): arrow-key movement and a score variable are things you have used before.
- Abstraction (keep only what matters): one sprite you control, one target, one score. Ignore lives, levels and extra enemies for now.
- Algorithms (steps in order): when the green flag starts the program, forever: move your sprite on the arrow keys; if your sprite is touching the target, change score by 1 and move the target to a new place.
That plan is short enough to build. Yours will be too.
Here is that plan as Scratch blocks. You are not building this one — it is the worked example, so you can see how the four steps turn into code:
when green flag clicked
set [score v] to (0)
forever
if <key (right arrow v) pressed?> then
change x by (10)
end
if <touching (Target v)?> then
change [score v] by (1)
broadcast [move target v]
end
end
Choose one build idea, or invent a close cousin of one of these:
- an animated scene (two sprites that take turns doing something)
- a short quiz round (ask a question, check the answer, change a score)
- a simple chase (catch a target, score goes up)
Open Scratch. Reopen a project you saved earlier if it helps, or start a fresh one. If your saved project is missing, ask your teacher or begin a new project from your plan.
- In your copybook, fill in a short plan for your idea using all four steps. Copy these four headings and complete each with one short line (like the chase example above):
- Decomposition: Pieces I will build: …
- Pattern recognition: I will reuse: …
- Abstraction: Only what matters for now: …
- Algorithms: In order, the program should: …
- Build only the first piece of that plan in Scratch. For a chase, that might be movement for the sprite you control. For a quiz, the question and answer check. For a scene, the first sprite's actions.
- Run what you have. Does that first piece match the algorithm you wrote?
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Scratch is developed by the Lifelong Kindergarten Group at the MIT Media Lab. It is available for free at https://scratch.mit.edu