Writing exam answers about algorithms

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A question says 'State the purpose of the algorithm'. Which answer is best?

A It sets Max to the first number, then uses a FOR loop and an IF to compare each number

B It finds the largest of 10 numbers entered by the user

2. A question says 'Describe the processes in the algorithm'. Which answer fits?

A Each mark is added to Total in a loop, then Total is divided by the number of marks

B It calculates the average mark

3. Which answer correctly identifies an error in the line IF Age = > 18 THEN?

A The algorithm is wrong and does not work

B The relational operator is written wrongly; it should be > or >=

4. The line Total = 0 is meant to set a variable. What is the correct suggestion to fix it?

A Replace = with the assignment arrow: Total ← 0

B Replace 0 with the word zero

5. A student must identify the error in a loop: FOR Count ← 1 TO 10 with no NEXT. Which is the precise answer?

A There is no NEXT Count to end the FOR loop

B The loop is not good

Match the Pairs

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

Left column		Right column
1State the purpose of the algorithm		ANot precise: it does not say what is wrong with the condition, for example that < should be <= so that 100 is included.
2Describe the processes in the algorithm		BToo vague: it lists features of the code but does not say what the algorithm does with the data, so it earns no marks for describing processes.
3Identify an error: name the exact line and say what is wrong with it		CWrite one sentence saying what the algorithm achieves overall, e.g. it finds the largest of 10 numbers entered
4Suggest a correction: write the replacement code using the right symbols in the condition		DLine 4: = is used for assignment, it should be ←
5The algorithm uses a loop and an IF and some variables.		ESay what the algorithm does with its data step by step, e.g. it adds each mark to Total and counts the marks
6Line 6 is wrong because the condition does not work.		FChange WHILE Mark > 100 to WHILE Mark >= 100

Definitions

command word

Fill in the Blanks

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

Error: Count = Count + 1 uses = to assign Correction: Count _ Count + 1

Error: Mark > 50 does not include 50 Correction: Mark _ 50

Error: OR used in a range check Correction: Age ≥ 11 ___ Age ≤ 16

Error: Total is not set to zero first Correction: Total ← _ before the loop

// Purpose: find the largest Mark IF Mark _ Largest THEN Largest ← Mark

Spot the Error

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

Question 1

A INPUT Mark

B Grade = "Fail"

C IF Mark >= 50 THEN

D Grade ← "Pass"

E ENDIF

Question 2

A Total ← 1

B INPUT Mark

C Total ← Total + Mark

D OUTPUT Total

Question 3

A Pass ← 0

B INPUT Mark

C // 50 or more is a pass

D IF Mark > 50 THEN

E Pass ← Pass + 1

F ENDIF

Question 4

A Number ← 1

B WHILE Number < 5 DO

C OUTPUT Number

D Number ← Number - 1

E ENDWHILE

Question 5

A INPUT Age

B Price ← 10

C IF Age < 5 AND Age > 65 THEN

D Price ← 0

E ENDIF

F OUTPUT Price

Answer Key

Writing exam answers about algorithms

Section A: Quick Questions

B — It finds the largest of 10 numbers entered by the user

A — Each mark is added to Total in a loop, then Total is divided by the number of marks

B — The relational operator is written wrongly; it should be > or >=

A — Replace = with the assignment arrow: Total ← 0

A — There is no NEXT Count to end the FOR loop

Section B: Match the Pairs

State the purpose of the algorithm → Write one sentence saying what the algorithm achieves overall, e.g. it finds the largest of 10 numbers entered

Describe the processes in the algorithm → Say what the algorithm does with its data step by step, e.g. it adds each mark to Total and counts the marks

Identify an error: name the exact line and say what is wrong with it → Line 4: = is used for assignment, it should be ←

Suggest a correction: write the replacement code using the right symbols in the condition → Change WHILE Mark > 100 to WHILE Mark >= 100

The algorithm uses a loop and an IF and some variables. → Too vague: it lists features of the code but does not say what the algorithm does with the data, so it earns no marks for describing processes.

Line 6 is wrong because the condition does not work. → Not precise: it does not say what is wrong with the condition, for example that < should be <= so that 100 is included.

Section C: Definitions

command word — The exam word that tells you what to write: state the purpose, describe the processes, identify the error, suggest the correction, each in precise terms.

Section D: Fill in the Blanks

Error: Count = Count + 1 uses = to assign
Correction: Count ← Count + 1

Error: Mark > 50 does not include 50
Correction: Mark ≥ 50

Error: OR used in a range check
Correction: Age ≥ 11 AND Age ≤ 16

Error: Total is not set to zero first
Correction: Total ← 0 before the loop

// Purpose: find the largest Mark
IF Mark > Largest THEN
  Largest ← Mark

Section E: Spot the Error

B — Identify the error: = is used for assignment. In pseudocode a value is assigned with the arrow, so the correction is Grade ← "Fail".

A — Identify the error: the total is not set to zero before totalling, so the answer is 1 too big. Suggest the correction: Total ← 0.

D — Identify the error: > leaves out a mark of exactly 50, but 50 or more is a pass. Suggest the correction: use the symbol >= in IF Mark >= 50 THEN.

D — Identify the error: Number goes down, so Number < 5 is always true and the loop never ends. Suggest the correction: Number ← Number + 1.

C — Identify the error: no age can be both under 5 and over 65, so AND is wrong and the condition is never true. Suggest the correction: use OR.