Brackets in pseudocode expressions

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which line correctly calculates the average of two marks, Mark1 and Mark2?

A Average ← (Mark1 + Mark2) / 2

B Average ← Mark1 + Mark2 / 2

2. A is 6 and B is 10. What is the value of A + B / 2?

A 8

B 11

3. A is 6 and B is 10. What is the value of (A + B) / 2?

A 8

B 11

4. Which statement about brackets in an expression is correct?

A The work inside the brackets is done first

B The work inside the brackets is done last

5. Which condition checks that a person is 18 or over AND has a ticket or a pass?

A Age >= 18 AND Ticket = TRUE OR Pass = TRUE

B Age >= 18 AND (Ticket = TRUE OR Pass = TRUE)

Match the Pairs

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

Left column		Right column
1Average ← (A + B) / 2		AResult ← A + B / 2
2IF (Age > 12) AND (Age < 20) OR (Member = TRUE) THEN		BAverage ← (Mark1 + Mark2 + Mark3) / 3
3Without brackets, division is done before addition, so only B is divided by 2		CWithout brackets, AND is worked out before OR, so the condition may not mean what was intended. Brackets are needed, such as (Age < 12 OR Age > 65) AND Member = TRUE.
4Brackets make an average of three marks correct by adding all the marks before dividing		DBrackets group the parts of the condition so the order in which AND and OR are applied is clear
5Average ← Total1 + Total2 / 2		EThe brackets are missing, so only Total2 is divided by 2 and Total1 is added afterwards. It should be (Total1 + Total2) / 2.
6IF Age < 12 OR Age > 65 AND Member = TRUE THEN		FAdds A and B first because of the brackets, then divides the total by 2 to give the average

Definitions

(A + B) / 2

Fill in the Blanks

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

Average ← _Mark1 + Mark2) / 2

Average ← (A + B + C) _ 3

IF (Day = "Sat" OR Day = "Sun") ___ Free = TRUE

DECLARE Average : REAL Average ← (Mark1 + Mark2) / _

IF Age > 15 AND _Pass OR Paid) THEN

Spot the Error

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

Question 1

A Average ← Mark1 + Mark2 / 2

B OUTPUT Average

C OUTPUT Mark1, Mark2

Question 2

A INPUT Vip, Cash, Card

B // must pay by Cash or Card

C IF Vip AND Cash OR Card THEN

D OUTPUT "Entry"

E ENDIF

Question 3

A INPUT A, B, C

B Mean ← (A + B + C / 3)

C OUTPUT Mean

Question 4

A Price ← 20

B Disc ← 5

C Qty ← 2

D Cost ← Price - Disc * Qty

E OUTPUT Cost

Question 5

A INPUT X

B // X must be from 1 to 10

C Valid ← TRUE

D IF NOT X > 0 AND X < 11 THEN

E Valid ← FALSE

F ENDIF

Answer Key

Brackets in pseudocode expressions

Section A: Quick Questions

A — Average ← (Mark1 + Mark2) / 2

B — 11

A — 8

A — The work inside the brackets is done first

B — Age >= 18 AND (Ticket = TRUE OR Pass = TRUE)

Section B: Match the Pairs

Average ← (A + B) / 2 → Adds A and B first because of the brackets, then divides the total by 2 to give the average

IF (Age > 12) AND (Age < 20) OR (Member = TRUE) THEN → Brackets group the parts of the condition so the order in which AND and OR are applied is clear

Without brackets, division is done before addition, so only B is divided by 2 → Result ← A + B / 2

Brackets make an average of three marks correct by adding all the marks before dividing → Average ← (Mark1 + Mark2 + Mark3) / 3

Average ← Total1 + Total2 / 2 → The brackets are missing, so only Total2 is divided by 2 and Total1 is added afterwards. It should be (Total1 + Total2) / 2.

IF Age < 12 OR Age > 65 AND Member = TRUE THEN → Without brackets, AND is worked out before OR, so the condition may not mean what was intended. Brackets are needed, such as (Age < 12 OR Age > 65) AND Member = TRUE.

Section C: Definitions

(A + B) / 2 — Brackets force the work inside to be done first, so A and B are added before dividing by 2. Without them, A + B / 2 divides B by 2 first. Use them in sums and AND/OR conditions.

Section D: Fill in the Blanks

Average ← (Mark1 + Mark2) / 2

Average ← (A + B + C) / 3

IF (Day = "Sat" OR Day = "Sun") AND
 Free = TRUE

DECLARE Average : REAL
Average ← (Mark1 + Mark2) / 2

IF Age > 15 AND (Pass OR Paid) THEN

Section E: Spot the Error

A — Without brackets, Mark2 / 2 is done first and then added to Mark1. The addition must be done first, so it needs brackets: (Mark1 + Mark2) / 2.

C — AND is done before OR, so this means (Vip AND Cash) OR Card. Anyone with Card would get in without being a Vip. The OR part needs brackets: Vip AND (Cash OR Card).

B — The bracket closes in the wrong place, so only C is divided by 3 and then added to A and B. The closing bracket should come before the division: (A + B + C) / 3.

D — Multiplication is done before subtraction, so only Disc is multiplied by Qty. The discount must be taken off first, so it needs brackets: (Price - Disc) * Qty.

D — Without brackets, NOT applies only to X > 0, not to the whole range check. The whole condition must be in brackets: NOT (X > 0 AND X < 11).