Tracing a counting algorithm

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Quick Questions

Shade in the A or B circle for each question.

1. A trace table row shows Mark = 40 and the condition Mark >= 50 is FALSE. What happens to Count on that row?

A Count stays the same

B Count goes up by 1

2. On a row where the condition is TRUE, Count was 2 on the row before. What is Count on this row?

A 2

B 3

3. Count ← 0. The marks 60, 45, 70 are checked with the condition Mark >= 50. What does OUTPUT Count show at the end?

A 2

B 3

4. Count is 1 on the previous row. Which trace table row is correct for Mark = 45 with the condition Mark >= 50?

A Mark 45 | Condition FALSE | Count 2

B Mark 45 | Condition FALSE | Count 1

5. The OUTPUT Count statement comes after the loop has ended. Which statement is correct?

A It shows the last value of Count in the trace table

B It shows the number of rows in the trace table

Match the Pairs

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

Left column		Right column
1Count ← Count + 1		AIF Mark >= 50 THEN Count ← Count + 1 ENDIF
2OUTPUT Count		BCount ← 0
3When the condition is FALSE, the counter stays the same, so the Count column repeats the previous value		CThe OUTPUT must show the final value of Count from the last row of the trace table, which is 3
4The counter must start at 0 so the first row of the trace table shows Count as 0 before any items are checked		DShows the final value of Count after the loop has finished, not the value on any one row
5Mark = 40 → condition (Mark >= 50) = TRUE, Count goes from 2 to 3		E40 is not greater than or equal to 50, so the condition is FALSE and Count should stay at 2
6Final row of trace table: Count = 3, but OUTPUT Count shows 2		FIn the trace table, Count goes up by 1 only on rows where the condition is TRUE

Definitions

Count ← Count + 1

Fill in the Blanks

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

IF Mark >= 50 THEN Count ← _____ + 1 ENDIF

IF Mark >= 50 THEN Count ← Count _ 1 ENDIF

IF Mark __ 50 THEN Count ← Count + 1 ENDIF

NEXT Index ______ Count

Count ← _ FOR Index ← 1 TO 5

Spot the Error

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

Question 1

A Pass ← 0

B FOR i ← 1 TO 5

C IF Mark[i] >= 50

D Pass ← Pass + 1

E ENDIF

F NEXT i

Question 2

A Count ← 0

B FOR i = 1 TO 6

C IF Score[i] > 10 THEN

D Count ← Count + 1

E ENDIF

F NEXT i

Question 3

A Count ← 0

B FOR i ← 1 TO 10

C IF Colour[i] ← "Red" THEN

D Count ← Count + 1

E ENDIF

F NEXT i

Question 4

A Count ← 1

B FOR i ← 1 TO 5

C Count ← Count + 1

D NEXT i

E OUTPUT Count

Question 5

A Count ← 0

B FOR i ← 1 TO 5

C IF Mark[i] >= 50 THEN

D Count ← Count + Mark[i]

E ENDIF

F NEXT i

Answer Key

Tracing a counting algorithm

Section A: Quick Questions

A — Count stays the same

B — 3

A — 2

B — Mark 45 | Condition FALSE | Count 1

A — It shows the last value of Count in the trace table

Section B: Match the Pairs

Count ← Count + 1 → In the trace table, Count goes up by 1 only on rows where the condition is TRUE

OUTPUT Count → Shows the final value of Count after the loop has finished, not the value on any one row

When the condition is FALSE, the counter stays the same, so the Count column repeats the previous value → IF Mark >= 50 THEN Count ← Count + 1 ENDIF

The counter must start at 0 so the first row of the trace table shows Count as 0 before any items are checked → Count ← 0

Mark = 40 → condition (Mark >= 50) = TRUE, Count goes from 2 to 3 → 40 is not greater than or equal to 50, so the condition is FALSE and Count should stay at 2

Final row of trace table: Count = 3, but OUTPUT Count shows 2 → The OUTPUT must show the final value of Count from the last row of the trace table, which is 3

Section C: Definitions

Count ← Count + 1 — In a trace table, Count goes up by 1 only on rows where the condition is TRUE. If it is FALSE, Count stays the same. The final value of Count is what the OUTPUT shows.

Section D: Fill in the Blanks

IF Mark >= 50 THEN
  Count ← Count + 1
ENDIF

IF Mark >= 50 THEN
  Count ← Count + 1
ENDIF

IF Mark >= 50 THEN
  Count ← Count + 1
ENDIF

NEXT Index
OUTPUT Count

Count ← 0
FOR Index ← 1 TO 5

Section E: Spot the Error

C — The IF line has no THEN. The condition is tested, and Pass only goes up when it is TRUE, so it must be written IF Mark[i] >= 50 THEN.

B — A FOR loop sets its start value with the assignment arrow, not =. It should be FOR i ← 1 TO 6.

C — The condition column in a trace table needs a comparison that is TRUE or FALSE. ← assigns a value instead. It should be IF Colour[i] = "Red" THEN.

A — Count must start at 0 before any items are counted. Starting at 1 makes every trace row and the final OUTPUT one too high. It should be Count ← 0.

D — This adds the mark to Count, which is totalling. Counting adds 1 each time the condition is TRUE. It should be Count ← Count + 1.