Counting in a loop (7a)

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Where should a counter be set to 0?

A Inside the loop, at the start of each repeat

B Before the loop starts

2. Which line adds 1 to a counter called Count?

A Count ← Count + 1

B Count + 1 ← Count

3. A program counts how many marks entered are 50 or more. Where does the counting line go?

A Outside the IF, so it runs for every mark

B Inside an IF Mark >= 50 THEN

4. A counter is never set to 0 before the loop. What is the problem?

A It starts with an unknown value, so the final count may be wrong

B The loop will run one extra time

5. Which statement about a counter is true?

A It goes up by 1 each time the thing being counted happens

B It adds the value the user typed in each time

Match the Pairs

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

Left column		Right column
1Counter ← 0		ACounter ← Counter + 1 is outside the IF, so it counts every number entered, not only the numbers greater than 5.
2Counter ← Counter + 1		BAdds 1 to the counter each time it runs, so the counter goes up by one
3Count only the marks that are 50 or more by putting the increase inside an IF that is true only for those marks		CInitialises the counter to zero before the loop starts, so counting begins from nothing
4Count only the valid entries by increasing the counter after a check shows the input is within the allowed range		DCounter ← 0 is inside the loop, so the counter resets to zero on every repeat and the count is lost. It must be set before the loop starts.
5FOR Index ← 1 TO 10 Counter ← 0 INPUT Number IF Number > 5 THEN Counter ← Counter + 1 ENDIF NEXT Index		EIF Age >= 11 AND Age <= 16 THEN ValidCount ← ValidCount + 1 ENDIF
6Counter ← 0 FOR Index ← 1 TO 10 INPUT Number Counter ← Counter + 1 IF Number > 5 THEN OUTPUT Number ENDIF NEXT Index		FIF Mark >= 50 THEN Passes ← Passes + 1 ENDIF

Definitions

Counter ← Counter + 1

Fill in the Blanks

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

Counter ← _ FOR Index ← 1 TO 10 INPUT Num

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

IF Score > 90 THEN Top ← ___ + 1 ENDIF

__ Age >= 18 THEN Adults ← Adults + 1 ENDIF

IF Num >= 1 ___ Num <= 10 THEN Valid ← Valid + 1 ENDIF

Spot the Error

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

Question 1

A Counter ← 0

B FOR Index ← 1 TO 5

C Counter ← Counter - 1

D NEXT Index

E OUTPUT Counter

Question 2

A DECLARE Counter : INTEGER

B Counter ← 1

C FOR Index ← 1 TO 10

D Counter ← Counter + 1

E NEXT Index

F OUTPUT Counter

Question 3

A Count ← 0

B INPUT Score

C WHILE Score <> -1 DO

D Counter ← Counter + 1

E INPUT Score

F ENDWHILE

Question 4

A Counter ← 0

B FOR Index ← 1 TO 20

C IF Index MOD 2 ← 0 THEN

D Counter ← Counter + 1

E ENDIF

F NEXT Index

Question 5

A DECLARE Attempts : INTEGER

B Attempts = 0

C REPEAT

D INPUT Age

E Attempts ← Attempts + 1

F UNTIL Age >= 0 AND Age <= 120

Answer Key

Counting in a loop (7a)

Section A: Quick Questions

B — Before the loop starts

A — Count ← Count + 1

B — Inside an IF Mark >= 50 THEN

A — It starts with an unknown value, so the final count may be wrong

A — It goes up by 1 each time the thing being counted happens

Section B: Match the Pairs

Counter ← 0 → Initialises the counter to zero before the loop starts, so counting begins from nothing

Counter ← Counter + 1 → Adds 1 to the counter each time it runs, so the counter goes up by one

Count only the marks that are 50 or more by putting the increase inside an IF that is true only for those marks → IF Mark >= 50 THEN Passes ← Passes + 1 ENDIF

Count only the valid entries by increasing the counter after a check shows the input is within the allowed range → IF Age >= 11 AND Age <= 16 THEN ValidCount ← ValidCount + 1 ENDIF

FOR Index ← 1 TO 10 Counter ← 0 INPUT Number IF Number > 5 THEN Counter ← Counter + 1 ENDIF NEXT Index → Counter ← 0 is inside the loop, so the counter resets to zero on every repeat and the count is lost. It must be set before the loop starts.

Counter ← 0 FOR Index ← 1 TO 10 INPUT Number Counter ← Counter + 1 IF Number > 5 THEN OUTPUT Number ENDIF NEXT Index → Counter ← Counter + 1 is outside the IF, so it counts every number entered, not only the numbers greater than 5.

Section C: Definitions

Counter ← Counter + 1 — A counter is a variable set to 0 before a loop, then increased by 1 with Counter ← Counter + 1 each time the thing being counted happens.

Section D: Fill in the Blanks

Counter ← 0
FOR Index ← 1 TO 10
   INPUT Num

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

IF Score > 90 THEN
   Top ← Top + 1
ENDIF

IF Age >= 18 THEN
   Adults ← Adults + 1
ENDIF

IF Num >= 1 AND Num <= 10 THEN
   Valid ← Valid + 1
ENDIF

Section E: Spot the Error

C — A counter goes up by 1 each time, so it needs Counter ← Counter + 1. Subtracting 1 makes the counter go down instead of counting.

B — A counter must be set to 0 before the loop starts. Starting at 1 makes the final count one too high. It should be Counter ← 0.

A — The variable initialised must have the same name as the counter used in the loop. Count is a different variable from Counter, so Counter is never set to 0. It should be Counter ← 0.

C — A condition compares values, so it must use the relational operator = and not the assignment arrow ←. It should be IF Index MOD 2 = 0 THEN.

B — Setting the starting value of the counter needs the assignment arrow, not the comparison =. With = the counter is never given the value 0. It should be Attempts ← 0.