Combining sequence, selection and iteration in one algorithm

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Quick Questions

Shade in the A or B circle for each question.

1. Where should Count <- 0 be written in an algorithm that counts passes in a FOR loop?

A Before the loop starts

B Inside the loop, on the first line

2. An algorithm must count how many of 30 marks are 50 or more. Which structure goes inside the loop?

A IF Mark >= 50 THEN Count <- Count + 1 ENDIF

B OUTPUT Count <- Count + 1 for every mark

3. Which statement is true about the three constructs in a complete algorithm?

A Selection repeats the input, iteration sets the counters, sequence decides which values to total

B Sequence sets up and outputs, iteration repeats, selection decides inside the loop

4. Where should OUTPUT "Passes: ", Count go if you want the final total of passes?

A After ENDFOR, once the loop has finished

B Inside the loop, before NEXT

5. Which is the correct order of the parts of a totalling algorithm?

A Loop with INPUT and IF, Total <- 0, then OUTPUT Total

B Total <- 0, loop with INPUT and IF, then OUTPUT Total

Match the Pairs

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

Left column		Right column
1Count <- 0 Total <- 0		AFOR Student <- 1 TO 30 INPUT Mark NEXT Student
2IF Mark >= 50 THEN Passes <- Passes + 1 ENDIF		BSelection inside the loop: only count the values that meet the condition
3Iteration repeats the input and processing steps a set number of times		COUTPUT is inside the loop, so it prints ten times. The result should be output once after NEXT.
4Results are output after the loop has finished, as the last part of the sequence		DSequence: set the counter and total to 0 before the loop starts
5FOR i <- 1 TO 10 Count <- 0 INPUT Num IF Num > 5 THEN Count <- Count + 1 ENDIF NEXT i		ECount is set to 0 inside the loop, so it is reset on every repeat and the final count is wrong. It must be set to 0 before the loop.
6FOR i <- 1 TO 10 INPUT Num Total <- Total + Num OUTPUT Total NEXT i		FNEXT Student OUTPUT "Passes: ", Passes

Definitions

sequence, selection, iteration

Fill in the Blanks

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

Total ← _ FOR Index ← 1 TO 5 INPUT Mark

FOR Student ← 1 TO 30 INPUT Mark __ Mark >= 50 THEN

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

NEXT Index OUTPUT "Total: ", _____

IF Mark > 50 THEN Total ← Total + ____ ENDIF

Spot the Error

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

Question 1

A Total <- 0

B FOR i <- 1 TO 5

C READ Price

D IF Price < 10 THEN

E Total <- Total + Price

F ENDIF

Question 2

A Total <- 0

B FOR i <- 1 TO 8

C INPUT Temp

D IF Temp > 30

E Total <- Total + Temp

F ENDIF

Question 3

A Count = 0

B FOR i <- 1 TO 20

C INPUT Age

D IF Age >= 18 THEN

E Count <- Count + 1

F ENDIF

Question 4

A IF Mark => 50 THEN

B Pass <- Pass + 1

C ENDIF

D NEXT i

E OUTPUT Pass

Question 5

A FOR i <- 1 TO 10

B INPUT Mark

C IF Mark >= 50 THEN

D Count <- Count + Mark

E ENDIF

F NEXT i

Answer Key

Combining sequence, selection and iteration in one algorithm

Section A: Quick Questions

A — Before the loop starts

A — IF Mark >= 50 THEN Count <- Count + 1 ENDIF

B — Sequence sets up and outputs, iteration repeats, selection decides inside the loop

A — After ENDFOR, once the loop has finished

B — Total <- 0, loop with INPUT and IF, then OUTPUT Total

Section B: Match the Pairs

Count <- 0 Total <- 0 → Sequence: set the counter and total to 0 before the loop starts

IF Mark >= 50 THEN Passes <- Passes + 1 ENDIF → Selection inside the loop: only count the values that meet the condition

Iteration repeats the input and processing steps a set number of times → FOR Student <- 1 TO 30 INPUT Mark NEXT Student

Results are output after the loop has finished, as the last part of the sequence → NEXT Student OUTPUT "Passes: ", Passes

FOR i <- 1 TO 10 Count <- 0 INPUT Num IF Num > 5 THEN Count <- Count + 1 ENDIF NEXT i → Count is set to 0 inside the loop, so it is reset on every repeat and the final count is wrong. It must be set to 0 before the loop.

FOR i <- 1 TO 10 INPUT Num Total <- Total + Num OUTPUT Total NEXT i → OUTPUT is inside the loop, so it prints ten times. The result should be output once after NEXT.

Section C: Definitions

sequence, selection, iteration — Set counters to 0 first (sequence), loop to read input (iteration), use IF inside the loop to pick values to count or total (selection), then OUTPUT the result after the loop.

Section D: Fill in the Blanks

Total ← 0
FOR Index ← 1 TO 5
   INPUT Mark

FOR Student ← 1 TO 30
   INPUT Mark
   IF Mark >= 50 THEN

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

NEXT Index
OUTPUT "Total: ", Total

IF Mark > 50 THEN
   Total ← Total + Mark
ENDIF

Section E: Spot the Error

C — Cambridge pseudocode reads a value with INPUT, not READ. The line should be INPUT Price, so each pass of the loop reads one price.

D — An IF statement needs THEN after its condition. The line should be IF Temp > 30 THEN, so the selection decides which temperatures are added to Total.

A — Assignment uses <-, not =. In Cambridge pseudocode = is a comparison. The counter must be set with Count <- 0 before the loop starts.

A — There is no => operator. 'Greater than or equal to' is written >=, so the line should be IF Mark >= 50 THEN.

D — To count the passes, Count must go up by 1 each time, not by the mark. The line should be Count <- Count + 1. Adding Mark would be totalling.