Session 16 — Score & Loops

Duration: 60 min · Format: live online

What you'll learn: by the end, you can create a score variable, use a forever loop to keep the game alive, and use broadcasts so sprites can talk to each other.

Soft skill focus — Critical thinking

Today you'll also grow Critical thinking. Good makers test their guesses instead of assuming — like whether set or change is the right block for a growing score.

Try this: before you run your score code, predict what will happen if you use set Score to 1 on every press. Then run it, watch it stick at 1, and compare to your guess. A "wrong" prediction is the most useful kind — it teaches you something.

Think about: What did you predict set would do, and what actually happened?

What you'll need

• Open Scratch and click Create — or open your project from Session 15 to build on. Either works.
• An idea to aim for: a "catch the apple" game — an apple sprite that keeps falling with a forever loop, and a Score that goes up when you press the space bar (you'll make it react to catching next session).

Hook

Think about these questions:

• In your favourite game, where does the score show up, and what makes it go up?
• The game keeps checking things over and over without stopping. How do you think it does that?
• How does one part of a game tell another part "hey, the player scored!"?

Here's the big idea: today you learn three superpowers — a variable to remember the score, a loop to keep the game running forever, and a broadcast so your sprites can send each other messages.

Teach — Variables hold a number

Here's how variables work:

• A variable is a box that remembers a number for you. A score is just a number that keeps changing.
• Go to the Variables section (orange), click Make a Variable, and name it Score. A Score box appears on the stage.

Build this in Scratch:

• Drag set [Score] to 0 and snap it under when green flag clicked. Every game starts the score at zero.
• Drag change [Score] by 1 under when [space] key pressed. Press space a few times — the score climbs.

⚠ Watch for the mix-up between set and change: set Score to 0 replaces the number; change Score by 1 adds to it. If you use set Score to 1 every press, the score gets stuck at 1. Try it once so you can see the difference.

Quick question: at the start of a game, should you set Score to 0 or change Score by 0? Why? (Answer: set to 0 — you want it to become zero, not just add nothing.)

Teach — Forever loops and broadcasts

A game never stops checking things — it does the same job over and over. That's a loop. The forever block (yellow, Control) repeats everything inside it, endlessly.

Use this diagram to picture the game loop — when the flag is clicked, a forever loop keeps moving sprites, checking collisions, and updating the score:

Build this in Scratch:

• Add a second sprite (an apple or ball). Give it when green flag clicked → forever → inside: change y by -5.
• Click the green flag. The apple falls, and falls, and falls — the loop keeps running. Without forever, it would move once and stop.
• Add if on edge, bounce or reset with set y to 150 inside the loop so it keeps coming back (either works — you'll polish it next session).

Now try broadcasts — how sprites talk to each other:

• A broadcast is like shouting a message across the room. One sprite broadcasts, any sprite can listen with when I receive.
• On the cat, add when [space] key pressed → broadcast [caught]. On the apple, add when I receive [caught] → play sound [Pop] and go to x: 0 y: 150 (jump back to the top).
• Press space — the message fires, the apple pops and resets.

Key idea: a variable remembers, a loop repeats, and a broadcast lets sprites send messages to each other.

Try it: if you take the change y by -5 out of the forever loop and just leave it on its own, how many times does the apple move? (Answer: once.)

Activity

Now build your own "catch" starter.

Build this, step by step:

1. Make a variable called Score (Variables → Make a Variable).
2. On the main sprite: when green flag clicked → set [Score] to 0.
3. Add a second sprite (apple, ball, star).
4. On the second sprite: when green flag clicked → forever → change y by -5.
5. Inside the same forever loop, add if y < -150 then → set y to 150 (so it loops back to the top). If if/then is new, just use set y to 150 after a few seconds for now.
6. On the main sprite: when [space] key pressed → change [Score] by 1 and broadcast [caught].
7. On the second sprite: when I receive [caught] → go to x: 0 y: 150 and play sound [Pop].
8. Click the green flag and test: the apple falls, space adds to the score and resets the apple.

If something's not working, check:

• A score that jumps straight to 1 and sticks — you used set Score to 1 instead of change Score by 1.
• A forever loop that "freezes" the editor — usually there's a forever with nothing that lets the screen update; adding a wait 0.1 seconds inside helps, or you simply need to click the flag to start it.
• Broadcasts that don't fire — the message name in broadcast and when I receive must match exactly (check the dropdown).

Tip: change the falling speed (change y by -5 → -8) and notice the game gets harder.

Check yourself

Try these — answers are after the arrow.

1. What is a variable, and what would you use one for in a game? → A box that remembers a number; use it for a score, a timer, lives, or a level number.
2. What does a forever loop do? → It repeats the blocks inside it endlessly, so the game keeps checking or moving without stopping.
3. How can one sprite tell another sprite that something happened? → With a broadcast — one sprite broadcasts a message, another runs when I receive that message.

Wrap-up

• In your own words, what is the difference between set and change?
• Try this at home — Level Up the Score: make the score go up by a different amount for a special action (for example, change Score by 5 on a rare key), or add a second variable like Lives. Bring it to Session 17.

Tips & extra challenges

• Watch out: it's easy to think "a forever loop is broken because it never ends." That's the point — games are meant to keep running. What you usually want is a loop that repeats but still lets other things happen; a tiny wait inside keeps it smooth.
• Want more? Try this: add a timer using a second variable — set Time to 30 at the start, then a separate loop that does wait 1 seconds → change Time by -1. Challenge: when Time hits 0, broadcast [game over] and have a sprite say "Time's up!" This is a sneak peek at the win/lose logic of Session 17.

Vocabulary

Resources

• Scratch — free, in your browser, no install (main tool).
• Scratch Ideas: Make It Fly / catch games — starter guides that use variables and loops.
• Scratch Wiki: Variables — friendly reference on what variables do.
• Scratch Wiki: Broadcast — how sprites send and receive messages.

Practice set

Practise on your own. Answers are after the arrow.

1. Make a variable called Score and set it to 0 when the green flag is clicked. → Variables → Make a Variable → name it Score; then when green flag clicked → set [Score] to 0.
2. Make the score go up by 1 every time you press the space bar. → when [space] key pressed → change [Score] by 1. (Use change, not set.)
3. Make a sprite fall down the screen forever. → when green flag clicked → forever → change y by -5.
4. When the falling sprite reaches the bottom, send it back to the top. → Inside the loop: if y < -150 then → set y to 150 (or go to x: 0 y: 150).
5. Make one sprite send a message and another sprite react to it. → Sprite A: broadcast [caught]. Sprite B: when I receive [caught] → do something (play a sound, hide, reset position).
6. Add a second variable called Lives, start it at 3, and lower it by 1 on a key press. → Make Lives; set [Lives] to 3 at start; when [key] pressed → change [Lives] by -1.

Going deeper (optional)

• Show the variable live on stage. Tick the checkbox next to a variable to show it, and use the display options (right-click the box) to make it a slider or a large readout. Think about where a real game shows its score, then place yours in a matching spot. This connects the code to how games actually look.
• Why broadcasts beat "just doing it in one script." In a real game, catching an apple has to do several things at once — add score, play a sound, reset the apple, maybe speed things up. A single broadcast can wake up many sprites at the same time, each doing its own job. Add a second when I receive [caught] on a different sprite (say, a cheering sprite) to feel this power.

Common mistakes & fixes

If it's not working, check these common mix-ups:

• Mistake: using set Score to 1 on every press, so the score never grows past 1. → Fix: switch to change Score by 1; set replaces, change adds.
• Mistake: forgetting to set Score to 0 at the start, so scores from the last play carry over. → Fix: always start with when green flag clicked → set [Score] to 0.
• Mistake: the broadcast name and the "when I receive" name don't match, so nothing happens. → Fix: pick the same message from both dropdowns; if unsure, make a new message with a clear name like caught.
• Mistake: a forever loop with no wait makes the sprite move too fast or the editor feel stuck. → Fix: add a small wait 0.1 seconds inside the loop, or lower the movement number.
• Mistake: putting the score-change inside the forever loop by accident, so it counts up thousands of times per second. → Fix: keep change Score by 1 under the key-press event, not inside the falling loop.

What's next

Session 17 — Levels & Challenge: you'll add if/then decisions, detect when sprites are touching, and build real win and lose conditions to make the game harder.