Describing the processes of a loop

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Quick Questions

Shade in the A or B circle for each question.

1. Which is the better description of FOR Count ← 1 TO 5 with Total ← Total + Count?

A The loop repeats 5 times and each time Count is added to Total

B The loop adds numbers together

2. Which phrase correctly describes the repeat part of: WHILE Mark <> -1 DO ... ENDWHILE?

A It repeats exactly 10 times

B It repeats until the user enters -1

3. A FOR loop runs from 1 to 20. Which describes it best?

A Condition-controlled: it repeats until a condition is met

B Count-controlled: it repeats 20 times

4. Which describes what happens to the data in: Total ← Total + Mark inside a loop?

A Each mark entered is added to Total

B Total is set to the first mark only

5. Which is the better answer to 'Describe the loop'?

A It repeats until Password is correct, asking for a new Password each time

B It is a loop that has a Password in it

Match the Pairs

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

Left column		Right column
1FOR Count ← 1 TO 10 Total ← Total + Count NEXT Count		ARepeats until the user enters -1, adding each mark to Total and then inputting the next mark
2WHILE Mark <> -1 DO Total ← Total + Mark INPUT Mark ENDWHILE		BIt does not say how many times the loop repeats or when it stops, so it is too vague.
3A count-controlled loop description gives the number of repeats: it repeats 5 times and each number input is added to Sum		CREPEAT INPUT Password UNTIL Password = "Secret"
4A condition-controlled loop description gives the stopping condition: it repeats until the password is correct, asking for a new password each time		DFOR Index ← 1 TO 5 INPUT Number Sum ← Sum + Number NEXT Index
5Description: "The loop adds numbers to Total."		ERepeats exactly 10 times, and each time round the current value of Count is added to Total
6Description: "The loop repeats 10 times."		FIt does not say what happens to the data each time round, such as which value is added or changed.

Definitions

Describing a loop

Fill in the Blanks

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

FOR Count ← 1 TO _ Total ← Total + Mark NEXT Count

WHILE Total < 100 DO Total ← _____ + Mark ENDWHILE

WHILE Count <= 5 DO Count ← Count _ 1 ENDWHILE

FOR Count ← 1 TO 10 ____ 2 OUTPUT Count NEXT Count

REPEAT Total ← Total + Mark _____ Total >= 100

Spot the Error

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

Question 1

A Total ← 0

B FOR Count ← 1 TO 5

C Mark ← INPUT

D Total ← Total + Mark

E NEXT Count

Question 2

A Count ← 0

B WHILE Count > 10 DO

C Count ← Count + 1

D ENDWHILE

Question 3

A Total ← 0

B FOR Day ← 1 TO 7

C INPUT Steps

D Total ← Total + Day

E NEXT Day

Question 4

A Attempts ← 0

B REPEAT

C INPUT Password

D Attempts ← Attempts - 1

E UNTIL Password = Secret

Question 5

A Total ← 0

B FOR Num ← 1 UNTIL 10

C Total ← Total + Num

D NEXT Num

E OUTPUT Total

Answer Key

Describing the processes of a loop

Section A: Quick Questions

A — The loop repeats 5 times and each time Count is added to Total

B — It repeats until the user enters -1

B — Count-controlled: it repeats 20 times

A — Each mark entered is added to Total

A — It repeats until Password is correct, asking for a new Password each time

Section B: Match the Pairs

FOR Count ← 1 TO 10 Total ← Total + Count NEXT Count → Repeats exactly 10 times, and each time round the current value of Count is added to Total

WHILE Mark <> -1 DO Total ← Total + Mark INPUT Mark ENDWHILE → Repeats until the user enters -1, adding each mark to Total and then inputting the next mark

A count-controlled loop description gives the number of repeats: it repeats 5 times and each number input is added to Sum → FOR Index ← 1 TO 5 INPUT Number Sum ← Sum + Number NEXT Index

A condition-controlled loop description gives the stopping condition: it repeats until the password is correct, asking for a new password each time → REPEAT INPUT Password UNTIL Password = "Secret"

Description: "The loop adds numbers to Total." → It does not say how many times the loop repeats or when it stops, so it is too vague.

Description: "The loop repeats 10 times." → It does not say what happens to the data each time round, such as which value is added or changed.

Section C: Definitions

Describing a loop — State how many times the loop repeats or the condition it stops on, and what happens to the data each time round, e.g. each mark is added to Total.

Section D: Fill in the Blanks

FOR Count ← 1 TO 5
   Total ← Total + Mark
NEXT Count

WHILE Total < 100 DO
   Total ← Total + Mark
ENDWHILE

WHILE Count <= 5 DO
   Count ← Count + 1
ENDWHILE

FOR Count ← 1 TO 10 STEP 2
   OUTPUT Count
NEXT Count

REPEAT
   Total ← Total + Mark
UNTIL Total >= 100

Section E: Spot the Error

C — INPUT is a keyword that comes first, followed by the variable. It should be INPUT Mark, so each of the 5 marks is read and then added to Total.

B — Count starts at 0, so Count > 10 is false straight away and the loop never runs. The loop repeats while Count < 10 and adds 1 to Count each time round.

D — Each pass should add the steps entered to Total, not the day number. It should be Total ← Total + Steps.

D — Attempts counts how many times the loop repeats until the password is correct, so it must go up by 1 each pass: Attempts ← Attempts + 1.

B — A count-controlled loop uses FOR ... TO to give the start and end values. UNTIL belongs to REPEAT loops. It should be FOR Num ← 1 TO 10.