Error: wrong relational operator

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Quick Questions

Shade in the A or B circle for each question.

1. A cinema lets in anyone aged 18 or over. Which condition is correct?

A IF Age > 18 THEN

B IF Age >= 18 THEN

2. The algorithm uses IF Age > 18 THEN to allow adults in. Which input value shows the error?

A Age = 18, the boundary value

B Age = 40, a typical value

3. A pass mark is 50 or more. Which line has a logic error?

A IF Mark > 50 THEN

B IF Mark >= 50 THEN

4. A bus fare discount is for people aged 16 or under. Which condition is correct?

A IF Age <= 16 THEN

B IF Age < 16 THEN

5. Which statement about the error Age > 18 instead of Age >= 18 is true?

A It is a syntax error: the program will not run

B It is a logic error: the program runs but gives the wrong result for 18

Match the Pairs

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

Left column		Right column
1IF Age > 18 THEN		A> should be >=. A person aged exactly 18 is wrongly rejected, because 18 > 18 is false. Test with the boundary value 18 and correct the operator to >=.
2IF Age >= 18 THEN		BIF Age <= 12 THEN
3To test a rule 'a pass mark is 50 or more', the boundary value 50 must be accepted, so use the operator that includes it.		C< should be <=. A Score of exactly 40 is wrongly missed, because 40 < 40 is false. Test with the boundary value 40 and correct the operator to <=.
4A rule says 'a child ticket is for ages up to and including 12'. The boundary value 12 must be included, so the operator needs an equals part.		DIF Mark >= 50 THEN
5IF Score < 40 THEN OUTPUT "Fail" ENDIF (Rule: 40 or less fails)		ECorrect operator for 'aged 18 or over': the boundary value 18 is accepted as well as everything above it.
6IF Age > 18 THEN OUTPUT "Can vote" ENDIF (Rule: 18 or over can vote)		FWrong at the boundary: a person aged exactly 18 is rejected, even though the rule says 18 or over should be accepted.

Definitions

Age >= 18

Fill in the Blanks

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

IF Age __ 18 THEN OUTPUT "Adult" ENDIF

IF Temp __ 0 THEN OUTPUT "Freezing: 0 counts" ENDIF

// Adults are 18 or over IF Age >= __ THEN OUTPUT "Adult"

Count ← 1 WHILE Count __ 10 DO Count ← Count + 1

IF Mark _ 40 THEN OUTPUT "Fail: 40 is a pass" ENDIF

Spot the Error

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

Question 1

A INPUT Age

B IF Age > 18 THEN

C OUTPUT "Can vote"

D ENDIF

Question 2

A DECLARE Mark : INTEGER

B OUTPUT "Enter mark"

C INPUT Mark

D IF Mark > 50 THEN

E OUTPUT "Pass"

F ENDIF

Question 3

A IF Age < 12 THEN

B Fare ← 5

C ENDIF

Question 4

A Count ← 0

B INPUT Score

C // 80 or more earns a merit

D IF Score > 80 THEN

E Count ← Count + 1

F ENDIF

Question 5

A IF Temp > 30 THEN

B OUTPUT "Hot day"

C ENDIF

Answer Key

Error: wrong relational operator

Section A: Quick Questions

B — IF Age >= 18 THEN

A — Age = 18, the boundary value

A — IF Mark > 50 THEN

A — IF Age <= 16 THEN

B — It is a logic error: the program runs but gives the wrong result for 18

Section B: Match the Pairs

IF Age > 18 THEN → Wrong at the boundary: a person aged exactly 18 is rejected, even though the rule says 18 or over should be accepted.

IF Age >= 18 THEN → Correct operator for 'aged 18 or over': the boundary value 18 is accepted as well as everything above it.

To test a rule 'a pass mark is 50 or more', the boundary value 50 must be accepted, so use the operator that includes it. → IF Mark >= 50 THEN

A rule says 'a child ticket is for ages up to and including 12'. The boundary value 12 must be included, so the operator needs an equals part. → IF Age <= 12 THEN

IF Score < 40 THEN OUTPUT "Fail" ENDIF (Rule: 40 or less fails) → < should be <=. A Score of exactly 40 is wrongly missed, because 40 < 40 is false. Test with the boundary value 40 and correct the operator to <=.

IF Age > 18 THEN OUTPUT "Can vote" ENDIF (Rule: 18 or over can vote) → > should be >=. A person aged exactly 18 is wrongly rejected, because 18 > 18 is false. Test with the boundary value 18 and correct the operator to >=.

Section C: Definitions

Age >= 18 — Using > instead of >= (or < instead of <=) is a logic error: the boundary value, such as Age 18, is wrongly rejected. Test the boundary value, then correct the operator.

Section D: Fill in the Blanks

IF Age >= 18 THEN
  OUTPUT "Adult"
ENDIF

IF Temp <= 0 THEN
  OUTPUT "Freezing: 0 counts"
ENDIF

// Adults are 18 or over
IF Age >= 18 THEN
  OUTPUT "Adult"

Count ← 1
WHILE Count <= 10 DO
  Count ← Count + 1

IF Mark < 40 THEN
  OUTPUT "Fail: 40 is a pass"
ENDIF

Section E: Spot the Error

B — Using > instead of >= wrongly rejects someone aged exactly 18, the boundary value. It should be IF Age >= 18 THEN.

D — A mark of exactly 50 should pass, but > rejects it. Testing the boundary value 50 shows the error. It should be IF Mark >= 50 THEN.

A — A 12 year old should get the child fare, but < excludes the boundary value 12. It should be IF Age <= 12 THEN.

D — A score of exactly 80 earns a merit, but > does not count it. The operator should be >=, so it should be IF Score >= 80 THEN.

A — A temperature of exactly 30 should count as a hot day. With > the boundary value 30 is missed. It should be IF Temp >= 30 THEN.