← ACARA Digital Technologies Years 5–6

Number guessing game algorithm

The guessing game loop: keep asking for a guess until it matches the secret number. Inside, decide too high, too low or correct, and add 1 to the count each time.

Part of: ACARA Digital Technologies Years 5–6 — Algorithms with Branching and Repetition — Module 37, ACARA Digital Technologies Years 7–8 — Algorithms, Flowcharts and Pseudocode — Module 37, ACARA Digital Technologies Years 7–8 — Tracing and Debugging Algorithms — Module 40

Understanding Number guessing game algorithm in ACARA Digital Technologies Years 5–6

What it does: This step makes the counter go up by 1 for each guess, so the game can tell the player how many tries it took. 70 is bigger than 50, so the guess is too high. The player should try a smaller number. To say too low, the algorithm must check guess < secret. The wrong version checks > twice, so 'too low' could never happen. No guesses have been made yet, so count starts at 0. It is not related to the secret number. Every guess is counted, including the winning one. Guesses 3, 9 and 7 make 3 guesses.

Common mistakes: The count must start at 0 because no guesses have been made yet. Starting at 1 makes the total one too many. It should be SET count TO 0. The player types a guess, not the secret number. Typing into secret would change the number being guessed. It should be INPUT guess.

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This module's key terms are also in a printable crossword (Modules 120–132) and word search (Modules 106–132).

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Learning

Duo

Which loop line keeps a number guessing game going until the player wins?

REPEAT UNTIL guess = secretREPEAT 1 TIME

Matches

REPEAT UNTIL guess > secret

↓

The loop stops when the guess is too high, not when it is correct. It should be REPEAT UNTIL guess = secret.

Applying

Meanings

Term

REPEAT UNTIL guess = secret

Meaning

The guessing game loop: keep asking for a guess until it matches the secret number. Inside, decide too high, too low or correct, and add 1 to the count each time.

Practice

SET secret TO 7

Testing

Gaps

SET count ←

Check Answer

Spots

1SET count TO 1

2REPEAT UNTIL guess = secret

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Quick Questions

1. Which loop line keeps a number guessing game going until the player wins?

A. REPEAT 1 TIME

B. REPEAT UNTIL guess = secret ✓

The game must repeat until the guess matches the secret number. We don't know how many guesses it will take, so a set number of repeats won't work.

2. The secret number is 50 and the player guesses 70. What should the algorithm say?

A. Too low

B. Too high ✓

70 is bigger than 50, so the guess is too high. The player should try a smaller number.

3. The secret number is 32 and the player guesses 18. What should the algorithm say?

A. Too low ✓

B. Too high

18 is smaller than 32, so the guess is too low. The player should try a bigger number.

4. Which set of decisions covers every possible guess?

A. IF guess > secret THEN too high, ELSE IF guess < secret THEN too low, ELSE correct ✓

B. IF guess > secret THEN too high, ELSE IF guess > secret THEN too low, ELSE correct

To say too low, the algorithm must check guess < secret. The wrong version checks > twice, so 'too low' could never happen.

5. Where should 'add 1 to count' go to count every guess?

A. Inside the loop, once for each guess ✓

B. After the loop, just once

The count must go up each time the player guesses, so the step belongs inside the loop. Putting it after the loop would only add 1 at the very end.

Match the Pairs

REPEAT UNTIL guess = secret → Keep asking for guesses again and again until the guess matches the secret number.

IF guess > secret THEN SAY "Too high" → If the guess is bigger than the secret number, tell the player the guess is too high.

Count every guess by adding 1 to the counter each time round the loop. → count ← count + 1

The decision for a wrong guess that is smaller than the secret number gives a 'too low' clue. → IF guess < secret THEN SAY "Too low"

REPEAT UNTIL guess > secret → The loop stops when the guess is too high, not when it is correct. It should be REPEAT UNTIL guess = secret.

SET count ← 0 (placed inside the loop) → The counter is reset to 0 on every go round the loop, so it never counts above 1. Set count to 0 once before the loop starts.

Key Term

REPEAT UNTIL guess = secret

The guessing game loop: keep asking for a guess until it matches the secret number. Inside, decide too high, too low or correct, and add 1 to the count each time.

Fill in the Blanks

1. SET secret ← 7 SET count ← 0 REPEAT UNTIL guess = secret

Hint: Type the number the guess counter starts at before any guesses are made.

2. REPEAT UNTIL guess = secret INPUT guess SET count ← count + 1

Hint: Type the keyword that keeps the loop going until the condition becomes true.

3. IF guess < secret THEN OUTPUT "Too low"

Hint: Type the comparison symbol that checks if the guess is smaller than the secret number.

4. INPUT guess SET count ← count + 1

Hint: Type the operator that adds one to the counter after each guess.

5. IF guess = secret THEN OUTPUT "Correct! Guesses: ", count

Hint: Type the name of the variable that holds how many guesses the player has made.

Spot the Error

Question 1

A SET count TO 1

B REPEAT UNTIL guess = secret

C INPUT guess

D ADD 1 TO count

Line A — The count must start at 0 because no guesses have been made yet. Starting at 1 makes the total one too many. It should be SET count TO 0.

Question 2

A SET secret TO 7

B SET count TO 0

C REPEAT UNTIL guess = secret

D INPUT secret

E ADD 1 TO count

Line D — The player types a guess, not the secret number. Typing into secret would change the number being guessed. It should be INPUT guess.

Question 3

A SET count TO 0

B REPEAT UNTIL guess ≠ secret

C INPUT guess

D ADD 1 TO count

Line B — The game must keep going until the guess is the same as the secret. With ≠ the loop would stop on a wrong guess. It should be REPEAT UNTIL guess = secret.

Question 4

A INPUT guess

B IF guess < secret THEN

C OUTPUT "Too high"

D ENDIF

Line B — The message says Too high, so the condition must check for a guess bigger than the secret. It should be IF guess > secret THEN.

Question 5

A REPEAT UNTIL guess = secret

B INPUT guess

C IF guess < secret

D OUTPUT "Too low"

E ADD 1 TO count

Line C — An IF decision needs the word THEN after the condition. It should be IF guess < secret THEN.

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