WHILE ... DO ... ENDWHILE loop (7a)

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Quick Questions

Shade in the A or B circle for each question.

1. When does a WHILE loop test its condition?

A After the statements inside the loop run

B Before the statements inside the loop run

2. Count ← 10 WHILE Count < 5 DO OUTPUT Count ENDWHILE What happens when this runs?

A The loop body runs once

B The loop body never runs

3. A WHILE loop repeats its statements for as long as the condition is...

A TRUE

B FALSE

4. Which keyword marks the end of a WHILE loop?

A ENDWHILE

B NEXT

5. Num ← 1 WHILE Num <= 5 DO OUTPUT Num ENDWHILE What is wrong with this loop?

A Num never changes, so the loop never ends

B The loop will never start

Match the Pairs

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

Left column		Right column
1WHILE Count <= 5 DO		AWHILE Count < 5 DO Count ← Count + 1 ENDWHILE
2ENDWHILE		BThe WHILE loop is closed with NEXT, which belongs to FOR loops. It must end with ENDWHILE.
3A WHILE loop tests its condition before the body, so if the condition is FALSE at the start the loop never runs		CNumber ← 10 WHILE Number < 5 DO OUTPUT Number ENDWHILE
4A variable in the condition must be changed inside the loop body so the condition eventually becomes FALSE and the loop ends		DMarks the end of the statements that belong to the WHILE loop and sends control back to test the condition again
5Count ← 1 WHILE Count <= 5 DO OUTPUT Count ENDWHILE		ECount is never changed inside the loop, so the condition stays TRUE forever and the loop never ends. Add Count ← Count + 1 before ENDWHILE.
6WHILE Count <= 5 DO Count ← Count + 1 NEXT		FTests the condition first and repeats the loop body only while Count is less than or equal to 5

Definitions

WHILE condition DO ... ENDWHILE

Fill in the Blanks

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

_____ Count < 5 DO Count ← Count + 1 ENDWHILE

WHILE Count < 5 DO Count ← Count + 1 ________

WHILE Total < 100 __ Total ← Total + 10 ENDWHILE

WHILE Count < 5 DO Count ← Count _ 1 ENDWHILE

WHILE Password __ "abc" DO INPUT Password ENDWHILE

Spot the Error

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

Question 1

A Count ← 1

B WHILE Count ← 5 DO

C OUTPUT Count

D Count ← Count + 1

E ENDWHILE

Question 2

A While Lives > 0 DO

B OUTPUT "Keep going"

C Lives ← Lives - 1

D ENDWHILE

Question 3

A Num ← 10

B WHILE Num > 0 DO

C Num ← Num + 2

D OUTPUT Num

E ENDWHILE

Question 4

A Score ← 0

B WHILE Score > 10 DO

C Score ← Score + 2

D OUTPUT Score

E ENDWHILE

Question 5

A Count = 1

B WHILE Count <= 4 DO

C OUTPUT Count * 2

D Count ← Count + 1

E ENDWHILE

Answer Key

WHILE ... DO ... ENDWHILE loop (7a)

Section A: Quick Questions

B — Before the statements inside the loop run

B — The loop body never runs

A — TRUE

A — ENDWHILE

A — Num never changes, so the loop never ends

Section B: Match the Pairs

WHILE Count <= 5 DO → Tests the condition first and repeats the loop body only while Count is less than or equal to 5

ENDWHILE → Marks the end of the statements that belong to the WHILE loop and sends control back to test the condition again

A WHILE loop tests its condition before the body, so if the condition is FALSE at the start the loop never runs → Number ← 10 WHILE Number < 5 DO OUTPUT Number ENDWHILE

A variable in the condition must be changed inside the loop body so the condition eventually becomes FALSE and the loop ends → WHILE Count < 5 DO Count ← Count + 1 ENDWHILE

Count ← 1 WHILE Count <= 5 DO OUTPUT Count ENDWHILE → Count is never changed inside the loop, so the condition stays TRUE forever and the loop never ends. Add Count ← Count + 1 before ENDWHILE.

WHILE Count <= 5 DO Count ← Count + 1 NEXT → The WHILE loop is closed with NEXT, which belongs to FOR loops. It must end with ENDWHILE.

Section C: Definitions

WHILE condition DO ... ENDWHILE — A loop that tests its condition first, then repeats its statements while the condition is TRUE. If it is FALSE at the start, the loop never runs. ENDWHILE marks the end of the loop.

Section D: Fill in the Blanks

WHILE Count < 5 DO
  Count ← Count + 1
ENDWHILE

WHILE Count < 5 DO
  Count ← Count + 1
ENDWHILE

WHILE Total < 100 DO
  Total ← Total + 10
ENDWHILE

WHILE Count < 5 DO
  Count ← Count + 1
ENDWHILE

WHILE Password <> "abc" DO
  INPUT Password
ENDWHILE

Section E: Spot the Error

B — A WHILE condition must compare values. ← is assignment, not a comparison. It should be WHILE Count <= 5 DO.

A — Cambridge pseudocode keywords are written in capital letters. It should be WHILE Lives > 0 DO.

C — Num goes up, so it moves away from 0 and the condition Num > 0 never becomes FALSE. The loop never ends. It should be Num ← Num - 2.

B — The condition is tested first. Score starts at 0, so Score > 10 is FALSE straight away and the loop never runs. It should be WHILE Score < 10 DO.

A — Giving a variable a starting value needs the assignment arrow. = is used to compare values. It should be Count ← 1.