Working out the purpose of an algorithm

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Quick Questions

Shade in the A or B circle for each question.

1. An algorithm sets total to 0, adds each price to total, then SHOWS total. What is its purpose?

A To count how many prices there are

B To work out the total cost of all the prices

2. What does the purpose of an algorithm tell us?

A What the whole algorithm achieves

B What one single step does

3. An algorithm sets count to 0, goes through each student, adds 1 to count if the student is present, then SHOWS count. Which sentence is its purpose?

A It shows the name of every student.

B It counts how many students are present.

4. An algorithm uses variables named highScore and playerScore. If playerScore is bigger than highScore, it copies playerScore into highScore. What do the names hint at?

A It keeps track of the highest score

B It adds up all the scores

5. An algorithm ends with: IF temperature < 15 THEN SHOW 'Take a jumper!'. What is the best purpose?

A To tell someone if they need a jumper

B To measure the temperature

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1SET total TO 0 REPEAT 5 TIMES ADD score TO total SHOW total		AThis only describes one part of the algorithm. A purpose says what the whole algorithm achieves, not just one step or variable.
2IF temperature > 30 THEN SHOW "Wear a hat" ELSE SHOW "No hat needed"		BIF age >= 18 THEN SHOW "You can vote" ELSE SHOW "Too young to vote"
3Variable names are clues to the purpose		CSET lapsRun TO 0 REPEAT UNTIL lapsRun = 10 ADD 1 TO lapsRun SHOW lapsRun
4The SHOW steps tell you what the algorithm achieves		DThis just repeats the steps in order. It does not say what the algorithm achieves.
5Purpose: it uses a variable called total		EPurpose: tells you whether to wear a hat
6Purpose: SET count TO 0, then REPEAT 3 TIMES, then SHOW count		FPurpose: adds up five scores and shows the total

Definitions

purpose

Fill in the Blanks

Complete each line of code by filling in the missing parts.

SET total ← 0 SET total ← total + 8 ____ total

SET lives ← 3 IF _____ = 0 THEN SHOW "Game over"

SET cost ← 35 SET change ← 50 _ cost SHOW change

SET score ← 62 IF score >= 50 THEN SHOW "Pass" ____ SHOW "Try again"

SET cheer ← "Hooray!" ______ 3 TIMES SHOW cheer

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A SET total TO 0

B ASK cost

C SET total TO total + price

D SHOW total

Question 2

A SET steps TO 0

B REPEAT 10 TIMES

C SET steps TO steps + 1

D SHOW step

Question 3

A SET evens TO 0

B ASK number

C IF number MOD 2 = 1 THEN

D SET evens TO evens + 1

E SHOW evens

Question 4

A SET highest TO 0

B ASK score

C IF score < highest THEN

D SET highest TO score

E SHOW highest

Question 5

A SET savings TO 0

B REPEAT 5 TIMES

C SET savings TO savings + 5

D SHOW "Money after 4 weeks"

Answer Key

Working out the purpose of an algorithm

Section A: Quick Questions

B — To work out the total cost of all the prices

A — What the whole algorithm achieves

B — It counts how many students are present.

A — It keeps track of the highest score

A — To tell someone if they need a jumper

Section B: Match the Pairs

SET total TO 0 REPEAT 5 TIMES ADD score TO total SHOW total → Purpose: adds up five scores and shows the total

IF temperature > 30 THEN SHOW "Wear a hat" ELSE SHOW "No hat needed" → Purpose: tells you whether to wear a hat

Variable names are clues to the purpose → SET lapsRun TO 0 REPEAT UNTIL lapsRun = 10 ADD 1 TO lapsRun SHOW lapsRun

The SHOW steps tell you what the algorithm achieves → IF age >= 18 THEN SHOW "You can vote" ELSE SHOW "Too young to vote"

Purpose: it uses a variable called total → This only describes one part of the algorithm. A purpose says what the whole algorithm achieves, not just one step or variable.

Purpose: SET count TO 0, then REPEAT 3 TIMES, then SHOW count → This just repeats the steps in order. It does not say what the algorithm achieves.

Section C: Definitions

purpose — What the whole algorithm achieves. Follow the steps, check what it SHOWS and read the variable names for clues, then say it in one sentence.

Section D: Fill in the Blanks

SET total ← 0
SET total ← total + 8
SHOW total

SET lives ← 3
IF lives = 0 THEN
  SHOW "Game over"

SET cost ← 35
SET change ← 50 - cost
SHOW change

SET score ← 62
IF score >= 50 THEN SHOW "Pass"
ELSE SHOW "Try again"

SET cheer ← "Hooray!"
REPEAT 3 TIMES
  SHOW cheer

Section E: Spot the Error

B — The algorithm adds up prices, so line 2 should ASK price. It asks for cost, but line 3 uses price, so the total would never be worked out properly.

D — The variable is called steps, not step. The purpose is to count 10 steps and show the answer, so line 4 should be SHOW steps.

C — The variable name evens tells us the purpose is to count even numbers. An even number has a remainder of 0 when divided by 2, so the test should be MOD 2 = 0.

C — The purpose is to find the highest score. The new score should replace highest only when it is bigger, so the test should be score > highest.

B — The SHOW step says the money is after 4 weeks, so the loop should repeat 4 times, one for each week. Repeating 5 times does not match the purpose.