Choosing FOR, WHILE or REPEAT

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. A program must output the numbers 1 to 10. Which loop is the best choice?

A FOR Count ← 1 TO 10

B WHILE Count > 10 DO

2. A program keeps asking for a password until the user types the right one. Which type of loop fits?

A A condition-controlled loop (WHILE or REPEAT)

B A count-controlled loop (FOR)

3. Which statement about REPEAT...UNTIL is true?

A The condition is tested at the start, so the loop body may never run

B The condition is tested at the end, so the loop body runs at least once

4. Which statement about WHILE...DO...ENDWHILE is true?

A The condition is tested at the end, so the body always runs once

B The condition is tested at the start, so the body might never run

5. A program must process exactly 30 test marks stored in an array. Which loop should you choose?

A FOR Index ← 1 TO 30

B REPEAT ... UNTIL the user stops typing

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		AFOR needs a known number as its end value, not a condition. A condition-based repeat needs WHILE or REPEAT.
2REPEAT ... UNTIL Guess = Secret		BA WHILE loop must end with ENDWHILE, not NEXT. NEXT belongs to a FOR loop.
3The condition is tested at the start, so the loop body may never run		CA count-controlled loop: the number of repeats is known (10) before it starts
4The number of repeats is known: read exactly 5 marks		DWHILE Password <> "open" DO
5WHILE Total < 100 DO INPUT Num Total ← Total + Num NEXT		EA condition-controlled loop that tests at the end, so the body always runs at least once
6FOR Count ← 1 TO Answer <> 5		FFOR Index ← 1 TO 5

Definitions

FOR, WHILE, REPEAT

Fill in the Blanks

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

___ Count ← 1 TO 5 OUTPUT Count NEXT Count

_____ Number < 0 DO INPUT Number ENDWHILE

REPEAT INPUT Guess _____ Guess = 7

WHILE Lives > 0 DO Lives ← Lives - 1 ________

FOR Day ← 1 TO 7 OUTPUT Day ____ Day

Spot the Error

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

Question 1

A FOR Student ← 1 TO 30

B INPUT Mark

C OUTPUT Mark

D ENDFOR

Question 2

A INPUT Password

B WHILE Password <> "open" DO

C INPUT Password

D NEXT Password

Question 3

A Guess ← 0

B WHILE

C INPUT Guess

D UNTIL Guess = 7

Question 4

A Total ← 0

B INPUT Mark

C WHILE Mark = -1 DO

D Total ← Total + Mark

E INPUT Mark

F ENDWHILE

Question 5

A Total ← 0

B FOR Num = 1 TO 10

C Total ← Total + Num

D NEXT Num

Answer Key

Choosing FOR, WHILE or REPEAT

Section A: Quick Questions

A — FOR Count ← 1 TO 10

A — A condition-controlled loop (WHILE or REPEAT)

B — The condition is tested at the end, so the loop body runs at least once

B — The condition is tested at the start, so the body might never run

A — FOR Index ← 1 TO 30

Section B: Match the Pairs

FOR Count ← 1 TO 10 → A count-controlled loop: the number of repeats is known (10) before it starts

REPEAT ... UNTIL Guess = Secret → A condition-controlled loop that tests at the end, so the body always runs at least once

The condition is tested at the start, so the loop body may never run → WHILE Password <> "open" DO

The number of repeats is known: read exactly 5 marks → FOR Index ← 1 TO 5

WHILE Total < 100 DO INPUT Num Total ← Total + Num NEXT → A WHILE loop must end with ENDWHILE, not NEXT. NEXT belongs to a FOR loop.

FOR Count ← 1 TO Answer <> 5 → FOR needs a known number as its end value, not a condition. A condition-based repeat needs WHILE or REPEAT.

Section C: Definitions

FOR, WHILE, REPEAT — Use FOR when the number of repeats is known. Use WHILE (tests at the start) or REPEAT (tests at the end) when repeating depends on a condition.

Section D: Fill in the Blanks

FOR Count ← 1 TO 5
  OUTPUT Count
NEXT Count

WHILE Number < 0 DO
  INPUT Number
ENDWHILE

REPEAT
  INPUT Guess
UNTIL Guess = 7

WHILE Lives > 0 DO
  Lives ← Lives - 1
ENDWHILE

FOR Day ← 1 TO 7
  OUTPUT Day
NEXT Day

Section E: Spot the Error

D — A FOR loop ends with NEXT and the loop variable, not ENDFOR. The line should be NEXT Student.

D — A WHILE loop (condition-controlled) must end with ENDWHILE. NEXT is only used to close a FOR loop.

B — The loop ends with UNTIL, so it must start with REPEAT, not WHILE. The line should be REPEAT.

C — WHILE repeats while its condition is true. With = -1 the loop would not run for normal marks. It should be WHILE Mark <> -1 DO.

B — A FOR loop sets its start value with the assignment arrow ←, not =. It should be FOR Num ← 1 TO 10.