Mod & Round — Scratch L3 · Advaslearning Hub

Where we are now: an even-number bonus rewards lucky rolls and the average score displays as a clean whole number. One more lesson polishes the final distance-from-target score and ships the game.

Learning Goals 3 min

By the end of this lesson you will be able to:

Explain what the () mod () block reports — the remainder left over after dividing the first number by the second.
Use round () to turn a messy decimal (like 3.7) into the nearest whole number.
Combine () mod () with () = () inside an if <> then to fire an event every Nth time — for example, a bonus pop-up every 5 points.

Warm-Up — sharing kuih equally 7 min

Aunty bought 10 pieces of kuih lapis for the cousins. There are 3 cousins. She wants to share equally, but she also wants to know how many pieces are left over for herself.

Two questions for you (don't peek at the answers yet):

How many whole pieces does each cousin get?
How many pieces are left over for Aunty?

Reveal the answer

Each cousin gets 3 pieces (because 3 × 3 = 9), and there is 1 piece left over for Aunty. In maths-speak: 10 ÷ 3 = 3 remainder 1. That "remainder 1" is exactly what () mod () reports. (10) mod (3) reports 1.

One more — Aniq is counting his steps to school. He counts 247 steps. He likes to chant a cheer every 10 steps. How can a script know exactly when the step count is a multiple of 10 — like 10, 20, 30, 240?

Reveal the answer

A number is a multiple of 10 when its remainder after dividing by 10 is zero. So (steps) mod (10) reports 0 at 10, 20, 30… and reports 1, 2, 3… in between. Combine it with () = () to test for that zero. You'll build exactly this in the worked example.

New Concept — remainders and rounding 15 min

The Operators palette has two small green blocks that most beginners ignore — until they need them. Once you see what they do, you spot uses everywhere.

Block 1 — () mod ()

"Mod" is short for modulo, a fancy word for remainder after division. The block has two round slots for numbers and reports a round number.


((10) mod (3))

Reports 1. Read it as: "ten divided by three, throw away the whole part, keep the leftover."

A few more values to lock the idea in:

(6) mod (3) reports 0 — 6 divides cleanly by 3, no leftover.
(7) mod (3) reports 1 — 7 is one past a clean multiple of 3.
(8) mod (3) reports 2 — 8 is two past.
(9) mod (3) reports 0 again — and the pattern repeats: 0, 1, 2, 0, 1, 2, 0…

That repeating 0, 1, 2… pattern is the magic. Mod gives you a counter that resets on its own.

Why this matters — every-Nth events

The most common Scratch use of mod is the every-Nth-time trick. Put mod inside a comparison, put the comparison inside an if-then:


if <((score) mod (5)) = (0)> then
  say [Bonus!] for (1) seconds
end

"Whenever the score is a multiple of 5 — 5, 10, 15, 20… — say Bonus." A milestone checker in three blocks.

Block 2 — round ()

The other block today is even smaller. round () takes one round slot and reports the nearest whole number.


(round (3.7))

Reports 4. round (3.2) reports 3. round (3.5) reports 4 (Scratch rounds halves up).

Why would you need this? Because division and square root and distance to all give you messy decimals like 17.3849. If you want to show that as a score on screen, a giant decimal looks ugly. Wrap it in round and you get a clean 17.


set [tens-away v] to (round ((distance to [Sprite1 v]) / (10)))

If the cat is 173 pixels from Sprite1, this stores 17 — "about 17 tens away". Much nicer than 17.3849.

Worked Example — adding an even/odd bonus to the Lucky Number Machine 12 min

We upgrade the Lucky Number Machine from Lesson 3. Two new things: mod adds a 3-point bonus when the total is even; round makes the average score display a clean whole number. Eight steps.

Stage plan. The even-bonus badge (bottom-left) fires when total mod 2 = 0. The average score panel (right) shows a rounded whole number. The cat (✏️) runs the whole updated script.

Step 1 — Open the Lucky Number Machine project

Open the project from Lesson 3. The cat has the random dice rolls and the total calculation from last time.

Step 2 — Make the variable and reset the score

Make a new variable score. At the top of the flag script, add set [score v] to (0) before the dice rolls. We'll add to score based on the total.

Step 3 — Set score to the total

After computing total, add: set [score v] to (total). The score starts equal to the total.

Step 4 — Add the even-number bonus using mod


if <((total) mod (2)) = (0)> then
  change [score v] by (3)
  say [Even bonus! +3] for (1) seconds
end

If the total is divisible by 2 (no remainder), add 3 to the score and tell the player.

Step 5 — Make an average score variable

Make a variable avgScore. Set it to ((total) + (score)) / (2) — the average of the raw total and the bonus score. This will be a decimal for most rolls.

Step 6 — Display the average rounded

After setting avgScore, wrap it in round when you say it:


say (join [Avg: ] (round (avgScore))) for (2) seconds

The round block strips the decimal. The player sees a clean number.

Step 7 — Full assembled flag script


when flag clicked
set [score v] to (0)
set [die1 v] to (pick random (1) to (6))
set [die2 v] to (pick random (1) to (6))
set [total v] to ((die1) + (die2))
set [score v] to (total)
if <((total) mod (2)) = (0)> then
  change [score v] by (3)
  say [Even bonus! +3] for (1) seconds
end
set [avgScore v] to (((total) + (score)) / (2))
say (join [Score: ] (score)) for (2) seconds
say (join [Avg: ] (round (avgScore))) for (2) seconds

Eleven blocks. Mod checks even/odd; round cleans the display. The machine now scores fairly.

Step 8 — Test it

Click the flag repeatedly. On even totals (2, 4, 6, 8, 10, 12) the cat shouts "Even bonus! +3" and the score jumps. On odd totals the bonus is silent. The average always shows a clean whole number. Scoring is now fair and tidy.

Try It Yourself — three drills 15 min

🟢 Easy

Goal: Make a sprite that says the rounded version of its own y-position whenever you click it. Drag the sprite around the Stage first, then click — the bubble should show a clean whole number like 87, not 86.7421.


when this sprite clicked
say (round (y position)) for (1) seconds

Think: Without round (), dragging the sprite a tiny bit gives weird decimals because the mouse never lands on perfect whole-number pixels. Round is the polish.

🟡 Medium

Goal: Build a stopwatch sprite that ticks once per second using wait (1) seconds, and plays a play sound [pop v] only on even seconds (2, 4, 6…). Use mod-equals-zero with 2.


when flag clicked
set [tick v] to (0)
forever
  wait (1) seconds
  change [tick v] by (1)
  if <((tick) mod (2)) = (0)> then
    play sound [pop v]
  end
end

Think: Change 2 to 3 and the pop plays every third tick. Mod's right slot is the "every how many?" dial.

🔴 Stretch

Goal: Make the cat alternate between two costumes by itself. Every odd score, costume "costume1". Every even score, costume "costume2". (Hint: (score) mod (2) reports 1 for odd, 0 for even.) Use if <> then else.


when this sprite clicked
change [score v] by (1)
if <((score) mod (2)) = (0)> then
  switch costume to [costume2 v]
else
  switch costume to [costume1 v]
end

Think: You just built a toggle — flip-flop behaviour from one mod block. This pattern is how blinkers, on/off switches, and zebra-stripe backgrounds get built.

Mini-Challenge — Mei's never-shouting cat 5 min

"Why won't it cheer?"

Mei copied the worked-example pattern but tweaked it for her own game. She wants the cat to shout "Hooray!" every 3 clicks. She clicks 3, 6, 9, 12 times — and nothing happens. Here's her stack:


when this sprite clicked
change [score v] by (1)
if <((score) mod (3)) = (1)> then
  say [Hooray!] for (1) seconds
end

Mei's stack. Looks fine — but the cheer fires at the wrong times.

What's actually happening, and how would you fix it?

Reveal one valid solution

Mei is comparing (score) mod (3) to 1, not 0. So the cheer fires when the score is 1, 4, 7, 10, 13… — one after every multiple of 3, not on them. The remainder is 0 exactly when score is a clean multiple of 3.

Fix: change the 1 to 0:


when this sprite clicked
change [score v] by (1)
if <((score) mod (3)) = (0)> then
  say [Hooray!] for (1) seconds
end

Now the cheer fires at score 3, 6, 9, 12 — the multiples of 3. Lesson: for "every Nth", always compare mod to 0. Comparing to any other number gives you the slots between the multiples.

🚀 Mission — Odd Bonus

Priya wants a second bonus rule for the Lucky Number Machine: a 2-point bonus when the total is odd (so neither roll dominates — even gets +3, odd gets +2). In your project, add the odd-number check right after the even-number check.

Use ((total) mod (2)) = (1) as the condition — when the remainder is 1, the total is odd.
Inside: change [score v] by (2) and say "Odd bonus! +2" for 1 second.
Make sure the even check and odd check are two separate if-thens, not an if-else (only one can ever be true at once, but the structure is cleaner this way).

✅ Done when: every roll now triggers exactly one bonus message — "Even bonus! +3" or "Odd bonus! +2" — and the score reflects it. Going further: add a third bonus: if the total equals the target exactly, say "Perfect match! +5" and add 5. Use (total) = (target) as the condition.

Recap 3 min

You met two small green Operators that punch above their weight. () mod () reports the remainder after dividing — and when you compare that remainder to zero, you've built an "every Nth time" detector for milestones, blinkers, alternating costumes, and rhythm. For the Lucky Number Machine, mod-equals-zero detects even totals and awards a bonus. round () trims an ugly decimal down to the nearest whole number, keeping the average score display tidy. Both blocks are tiny in size and huge in usefulness.

Modulo (mod): The leftover after one number is divided by another. (10) mod (3) reports 1 because 10 ÷ 3 is 3 with 1 left over.
Multiple: A number you get by multiplying another whole number. Multiples of 5 are 0, 5, 10, 15, 20… A number is a multiple of N when (it) mod (N) = 0.
Remainder: The "left over" part of a division that doesn't go in evenly. The output of () mod ().
Round: To turn a decimal into the nearest whole number. round (3.7) reports 4; round (3.2) reports 3.
Milestone: A specific score, time, or count worth celebrating. Mod-equals-zero is the standard way to detect them inside a forever loop.

Homework 2 min

The Every-Third-Click Game. Build a one-sprite project that turns clicks into a tiny rhythm.

One sprite (any costume), one variable clicks, set to 0 on flag.
When the sprite is clicked, change clicks by 1.
On every 3rd click, play play sound [pop v].
On every 10th click, also say say [Score milestone!] for (1) seconds.
Add one more sprite anywhere on the Stage that continuously shows say (round ((clicks) / (3))) — "how many full sets of 3 have I clicked?". Use forever + say (the watcher version, no time).

Save as HW-L3-04-Mod-And-Round.sb3. Click your cat 30 times in a row — you should hear 10 pops, see 3 "milestone" speech bubbles, and the second sprite should end up showing 10.

Bring back next class:

The .sb3 file.
Your answer to: "At click number 9, what does ((clicks) mod (3)) report, and what does (round ((clicks) / (3))) report? Explain in one sentence each."

Heads up for next class: SCR-L03-05 meets the compound [abs v] of () block. We'll use abs to measure exactly how far the Lucky Number Machine's total lands from the target — and floor to give the final polished score before we ship the game.

Learning Goals 3 min

By the end of this lesson you will be able to:

Explain what the () mod () block reports — the remainder left over after dividing the first number by the second.
Use round () to turn a messy decimal (like 3.7) into the nearest whole number.
Combine () mod () with () = () inside an if <> then to fire an event every Nth time — for example, a bonus pop-up every 5 points.

Warm-Up — sharing kuih equally 7 min

Aunty bought 10 pieces of kuih lapis for the cousins. There are 3 cousins. She wants to share equally, but she also wants to know how many pieces are left over for herself.

Two questions for you (don't peek at the answers yet):

How many whole pieces does each cousin get?
How many pieces are left over for Aunty?

Reveal the answer

New Concept — remainders and rounding 15 min

The Operators palette has two small green blocks that most beginners ignore — until they need them. Once you see what they do, you spot uses everywhere.

Block 1 — () mod ()

"Mod" is short for modulo, a fancy word for remainder after division. The block has two round slots for numbers and reports a round number.


((10) mod (3))

Reports 1. Read it as: "ten divided by three, throw away the whole part, keep the leftover."

A few more values to lock the idea in:

(6) mod (3) reports 0 — 6 divides cleanly by 3, no leftover.
(7) mod (3) reports 1 — 7 is one past a clean multiple of 3.
(8) mod (3) reports 2 — 8 is two past.
(9) mod (3) reports 0 again — and the pattern repeats: 0, 1, 2, 0, 1, 2, 0…

That repeating 0, 1, 2… pattern is the magic. Mod gives you a counter that resets on its own.

Why this matters — every-Nth events

The most common Scratch use of mod is the every-Nth-time trick. Put mod inside a comparison, put the comparison inside an if-then:


if <((score) mod (5)) = (0)> then
  say [Bonus!] for (1) seconds
end

"Whenever the score is a multiple of 5 — 5, 10, 15, 20… — say Bonus." A milestone checker in three blocks.

Block 2 — round ()

The other block today is even smaller. round () takes one round slot and reports the nearest whole number.


(round (3.7))

Reports 4. round (3.2) reports 3. round (3.5) reports 4 (Scratch rounds halves up).


set [tens-away v] to (round ((distance to [Sprite1 v]) / (10)))

If the cat is 173 pixels from Sprite1, this stores 17 — "about 17 tens away". Much nicer than 17.3849.

Worked Example — adding an even/odd bonus to the Lucky Number Machine 12 min

We upgrade the Lucky Number Machine from Lesson 3. Two new things: mod adds a 3-point bonus when the total is even; round makes the average score display a clean whole number. Eight steps.

Stage plan. The even-bonus badge (bottom-left) fires when total mod 2 = 0. The average score panel (right) shows a rounded whole number. The cat (✏️) runs the whole updated script.

Step 1 — Open the Lucky Number Machine project

Open the project from Lesson 3. The cat has the random dice rolls and the total calculation from last time.

Step 2 — Make the variable and reset the score

Make a new variable score. At the top of the flag script, add set [score v] to (0) before the dice rolls. We'll add to score based on the total.

Step 3 — Set score to the total

After computing total, add: set [score v] to (total). The score starts equal to the total.

Step 4 — Add the even-number bonus using mod


if <((total) mod (2)) = (0)> then
  change [score v] by (3)
  say [Even bonus! +3] for (1) seconds
end

If the total is divisible by 2 (no remainder), add 3 to the score and tell the player.

Step 5 — Make an average score variable

Make a variable avgScore. Set it to ((total) + (score)) / (2) — the average of the raw total and the bonus score. This will be a decimal for most rolls.

Step 6 — Display the average rounded

After setting avgScore, wrap it in round when you say it:


say (join [Avg: ] (round (avgScore))) for (2) seconds

The round block strips the decimal. The player sees a clean number.

Step 7 — Full assembled flag script


when flag clicked
set [score v] to (0)
set [die1 v] to (pick random (1) to (6))
set [die2 v] to (pick random (1) to (6))
set [total v] to ((die1) + (die2))
set [score v] to (total)
if <((total) mod (2)) = (0)> then
  change [score v] by (3)
  say [Even bonus! +3] for (1) seconds
end
set [avgScore v] to (((total) + (score)) / (2))
say (join [Score: ] (score)) for (2) seconds
say (join [Avg: ] (round (avgScore))) for (2) seconds

Eleven blocks. Mod checks even/odd; round cleans the display. The machine now scores fairly.

Step 8 — Test it

Try It Yourself — three drills 15 min

🟢 Easy


when this sprite clicked
say (round (y position)) for (1) seconds

Think: Without round (), dragging the sprite a tiny bit gives weird decimals because the mouse never lands on perfect whole-number pixels. Round is the polish.

🟡 Medium

Goal: Build a stopwatch sprite that ticks once per second using wait (1) seconds, and plays a play sound [pop v] only on even seconds (2, 4, 6…). Use mod-equals-zero with 2.


when flag clicked
set [tick v] to (0)
forever
  wait (1) seconds
  change [tick v] by (1)
  if <((tick) mod (2)) = (0)> then
    play sound [pop v]
  end
end

Think: Change 2 to 3 and the pop plays every third tick. Mod's right slot is the "every how many?" dial.

🔴 Stretch


when this sprite clicked
change [score v] by (1)
if <((score) mod (2)) = (0)> then
  switch costume to [costume2 v]
else
  switch costume to [costume1 v]
end

Think: You just built a toggle — flip-flop behaviour from one mod block. This pattern is how blinkers, on/off switches, and zebra-stripe backgrounds get built.

Mini-Challenge — Mei's never-shouting cat 5 min

"Why won't it cheer?"

Mei copied the worked-example pattern but tweaked it for her own game. She wants the cat to shout "Hooray!" every 3 clicks. She clicks 3, 6, 9, 12 times — and nothing happens. Here's her stack:


when this sprite clicked
change [score v] by (1)
if <((score) mod (3)) = (1)> then
  say [Hooray!] for (1) seconds
end

Mei's stack. Looks fine — but the cheer fires at the wrong times.

What's actually happening, and how would you fix it?

Reveal one valid solution

Fix: change the 1 to 0:


when this sprite clicked
change [score v] by (1)
if <((score) mod (3)) = (0)> then
  say [Hooray!] for (1) seconds
end

Now the cheer fires at score 3, 6, 9, 12 — the multiples of 3. Lesson: for "every Nth", always compare mod to 0. Comparing to any other number gives you the slots between the multiples.

🚀 Mission — Odd Bonus

Use ((total) mod (2)) = (1) as the condition — when the remainder is 1, the total is odd.
Inside: change [score v] by (2) and say "Odd bonus! +2" for 1 second.
Make sure the even check and odd check are two separate if-thens, not an if-else (only one can ever be true at once, but the structure is cleaner this way).

Recap 3 min

Modulo (mod): The leftover after one number is divided by another. (10) mod (3) reports 1 because 10 ÷ 3 is 3 with 1 left over.
Multiple: A number you get by multiplying another whole number. Multiples of 5 are 0, 5, 10, 15, 20… A number is a multiple of N when (it) mod (N) = 0.
Remainder: The "left over" part of a division that doesn't go in evenly. The output of () mod ().
Round: To turn a decimal into the nearest whole number. round (3.7) reports 4; round (3.2) reports 3.
Milestone: A specific score, time, or count worth celebrating. Mod-equals-zero is the standard way to detect them inside a forever loop.

Homework 2 min

The Every-Third-Click Game. Build a one-sprite project that turns clicks into a tiny rhythm.

One sprite (any costume), one variable clicks, set to 0 on flag.
When the sprite is clicked, change clicks by 1.
On every 3rd click, play play sound [pop v].
On every 10th click, also say say [Score milestone!] for (1) seconds.
Add one more sprite anywhere on the Stage that continuously shows say (round ((clicks) / (3))) — "how many full sets of 3 have I clicked?". Use forever + say (the watcher version, no time).

Save as HW-L3-04-Mod-And-Round.sb3. Click your cat 30 times in a row — you should hear 10 pops, see 3 "milestone" speech bubbles, and the second sprite should end up showing 10.

Bring back next class:

The .sb3 file.
Your answer to: "At click number 9, what does ((clicks) mod (3)) report, and what does (round ((clicks) / (3))) report? Explain in one sentence each."