← IGCSE Computer Science Paper 2

CASE clauses with ranges and several statements

In a CASE clause, value1 TO value2 matches a whole range, such as 1 TO 9. Indented statements under the clause all run. Ranges in one CASE must not overlap.

Part of: IGCSE Computer Science 0478 — 8.1b Sequence, Selection and Iteration — Module 21

Understanding CASE clauses with ranges and several statements in IGCSE Computer Science Paper 2

What it does: The range is written as value1 TO value2, followed by a colon and the statement to run. The ranges 0 TO 49 and 50 TO 100 share no values, so every mark matches exactly one clause. A CASE clause lists values or a range using TO. It does not use relational operators like < in the clause. Ranges in one CASE must not overlap. In the wrong pair, 50 would match both clauses. All the indented statements under a matching clause run, one after the other. Range ends are included. 75 is the first value of 75 TO 100 and is outside 50 TO 74.

Common mistakes: A range in a CASE clause is written with TO, not a hyphen. It should be 40 TO 69 : OUTPUT "B". The colon is missing after the range. A clause must be written 1 TO 9 : OUTPUT "Low".

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This module's key terms are also in a printable crossword (Modules 369–378) and word search (Modules 358–378).

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Learning

Duo

Which CASE clause correctly matches every whole number from 1 to 9?

1 - 9 : OUTPUT "Low"1 TO 9 : OUTPUT "Low"

Matches

0 TO 50 : grade <- "F" 50 TO 100 : grade <- "P"

↓

The ranges overlap because 50 is in both 0 TO 50 and 50 TO 100. The first range should end at 49.

Applying

Meanings

Term

1 TO 9 :

Meaning

In a CASE clause, value1 TO value2 matches a whole range, such as 1 TO 9. Indented statements under the clause all run. Ranges in one CASE must not overlap.

Practice

CASE OF Mark

Testing

Gaps

0 49 : OUTPUT "Fail"

Check Answer

Spots

2 70 TO 100 : OUTPUT "A"

3 40 - 69 : OUTPUT "B"

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Quick Questions

1. Which CASE clause correctly matches every whole number from 1 to 9?

A. 1 TO 9 : OUTPUT "Low" ✓

B. 1 - 9 : OUTPUT "Low"

A range in a CASE clause is written value1 TO value2, followed by a colon and the statement.

2. Which clause is a valid grade band for marks from 50 up to 69?

A. 50 < Mark < 69 : Grade <- "B"

B. 50 TO 69 : Grade <- "B" ✓

A CASE clause lists values or a range using TO. It does not use relational operators like < in the clause.

3. Which pair of CASE clauses is written correctly for marks 0 to 100?

A. 0 TO 49 : and 50 TO 100 : ✓

B. 0 TO 50 : and 50 TO 100 :

Ranges in one CASE must not overlap. In the wrong pair, 50 would match both clauses.

4. A clause has two indented statements under it. What happens when its range matches?

A. Only the first statement runs

B. Both indented statements run, in order ✓

All the indented statements under a matching clause run, one after the other.

5. The clauses are 0 TO 49, 50 TO 74 and 75 TO 100. Mark is 75. Which clause runs?

A. 75 TO 100 ✓

B. 50 TO 74

Range ends are included. 75 is the first value of 75 TO 100 and is outside 50 TO 74.

Match the Pairs

1 TO 9 : → A CASE clause that matches any value from 1 up to 9, including both 1 and 9

70 TO 100 : grade <- "A" OUTPUT grade → A range clause whose two indented statements both run when the value is between 70 and 100

A range clause for the grade band 50 to 69 that sets the grade to B → 50 TO 69 : grade <- "B"

Ranges in the same CASE must not overlap, so each mark belongs to only one band → 0 TO 49 : 50 TO 100 :

0 TO 50 : grade <- "F" 50 TO 100 : grade <- "P" → The ranges overlap because 50 is in both 0 TO 50 and 50 TO 100. The first range should end at 49.

CASE OF mark 1 - 9 : OUTPUT "Low" ENDCASE → A range must be written with the keyword TO, not a hyphen. It should be 1 TO 9 :

Key Term

1 TO 9 :

In a CASE clause, value1 TO value2 matches a whole range, such as 1 TO 9. Indented statements under the clause all run. Ranges in one CASE must not overlap.

Fill in the Blanks

1. CASE OF Score 0 TO 49 : OUTPUT "Fail" ENDCASE

Hint: Type the keyword that joins the lowest and highest values of a range in a CASE clause.

2. CASE OF Mark 50 TO 69 : OUTPUT "Merit" ENDCASE

Hint: Type the keyword that displays a message when the Mark falls in this range.

3. CASE OF Mark 1 TO 9 : Total <- Total + Mark OUTPUT Total

Hint: Type the variable that was updated by the statement on the line above, which is part of the same clause.

4. 0 TO 49 : Grade <- "F" 50 TO 100 : Grade <- "P" ENDCASE

Hint: Type the number that starts the next grade band, with no overlap and no gap after the previous range ends.

5. CASE OF Mark 1 TO 9 : OUTPUT "Low" ENDCASE

Hint: Type the keyword that closes the whole CASE structure.

Spot the Error

Question 1

A CASE OF Mark

B 70 TO 100 : OUTPUT "A"

C 40 - 69 : OUTPUT "B"

D ENDCASE

Line C — A range in a CASE clause is written with TO, not a hyphen. It should be 40 TO 69 : OUTPUT "B".

Question 2

A CASE OF Score

B 1 TO 9 OUTPUT "Low"

C 10 TO 99 : OUTPUT "High"

D ENDCASE

Line B — The colon is missing after the range. A clause must be written 1 TO 9 : OUTPUT "Low".

Question 3

A CASE OF Mark

B 70 TO 100 :

C OUTPUT "Pass"

D Passes <- Pass + 1

E ENDCASE

Line D — The statement must add 1 to the same variable it assigns to. Pass is a different, undeclared variable. It should be Passes <- Passes + 1.

Question 4

A CASE Mark

B 50 TO 100 : OUTPUT "Pass"

C OTHERWISE : OUTPUT "Fail"

D ENDCASE

Line A — The CASE statement must start with CASE OF followed by the variable. The word OF is missing, so it should be CASE OF Mark.

Question 5

A CASE OF Age

B 0 TO 13 : OUTPUT "Child"

C 13 TO 19 : OUTPUT "Teen"

D ENDCASE

Line B — Ranges in one CASE must not overlap. 0 TO 13 includes 13, which is also in 13 TO 19. It should be 0 TO 12.

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