← IGCSE Computer Science Paper 2

OTHERWISE in a CASE statement (8.1b)

The last clause of a CASE statement. It runs when the variable matches none of the listed values, e.g. OTHERWISE : OUTPUT "Invalid choice". Without it, nothing happens if no value matches.

Part of: IGCSE Computer Science 0478 — 8.1b Sequence, Selection and Iteration — Module 20

Understanding OTHERWISE in a CASE statement (8.1b) in IGCSE Computer Science Paper 2

What it does: The OTHERWISE clause comes after every listed value and directly before ENDCASE. This line is the catch-all that reports an invalid choice when no listed value matches. OTHERWISE comes last. It only runs when none of the values above it matched. OTHERWISE is followed by a colon and then the statement to run, just like the other CASE clauses. It does not use ELSE.

Common mistakes: Each CASE clause needs a colon between the value and the statement. It should be 1 : OUTPUT "Start". A CASE statement starts with CASE OF followed by the variable. OF is missing; it should be CASE OF Menu. Without it, the OTHERWISE clause has no valid CASE to belong to.

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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

Where does OTHERWISE go in a CASE statement?

As the first clause, before the listed valuesAs the last clause, after all the listed values

Matches

CASE OF Choice OTHERWISE : OUTPUT "Invalid choice" 1 : OUTPUT "Start" ENDCASE

↓

OTHERWISE is placed before the listed value. It must be the last clause, so move it below 1 : OUTPUT "Start".

Applying

Meanings

Term

OTHERWISE

Meaning

The last clause of a CASE statement. It runs when the variable matches none of the listed values, e.g. OTHERWISE : OUTPUT "Invalid choice". Without it, nothing happens if no value matches.

Practice

CASE OF Choice

Testing

Gaps

: OUTPUT "Invalid choice"

Check Answer

Spots

1CASE OF Choice

2 1 OUTPUT "Start"

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Quick Questions

1. Where does OTHERWISE go in a CASE statement?

A. As the last clause, after all the listed values ✓

B. As the first clause, before the listed values

OTHERWISE comes last. It only runs when none of the values above it matched.

2. When does the OTHERWISE clause run?

A. Every time the CASE statement runs

B. When the variable matches none of the listed values ✓

OTHERWISE is a catch-all. It is skipped if one of the listed values matches.

3. Choice is 7 and the CASE only lists 1, 2 and 3, with no OTHERWISE. What happens?

A. Nothing happens, no clause runs ✓

B. The program stops with an error message

A CASE without OTHERWISE does nothing when no value matches. The program carries on with the next statement.

4. Which line is the correct way to write an OTHERWISE clause?

A. OTHERWISE OUTPUT "Invalid choice" ELSE

B. OTHERWISE : OUTPUT "Invalid choice" ✓

OTHERWISE is followed by a colon and then the statement to run, just like the other CASE clauses. It does not use ELSE.

5. Choice is 2 and the CASE has 2 : OUTPUT "Option 2" and OTHERWISE : OUTPUT "Invalid choice". What is output?

A. Option 2 ✓

B. Option 2 and Invalid choice

Only one clause runs. Since 2 matched, OTHERWISE is skipped.

Match the Pairs

OTHERWISE : OUTPUT "Invalid choice" → Runs and displays an error message when the CASE variable matches none of the listed values

CASE OF Choice 1 : OUTPUT "Start" 2 : OUTPUT "Quit" ENDCASE → A CASE with no OTHERWISE, so nothing happens if Choice is 3

OTHERWISE must be the last clause, placed after all the listed values and just before ENDCASE → CASE OF Grade 'A' : OUTPUT "Top" 'B' : OUTPUT "Good" OTHERWISE : OUTPUT "Try again" ENDCASE

Use OTHERWISE to catch invalid menu choices and tell the user → OTHERWISE : OUTPUT "Invalid choice"

CASE OF Choice OTHERWISE : OUTPUT "Invalid choice" 1 : OUTPUT "Start" ENDCASE → OTHERWISE is placed before the listed value. It must be the last clause, so move it below 1 : OUTPUT "Start".

OTHERWISE OUTPUT "Invalid choice" → The colon is missing after OTHERWISE. It should be OTHERWISE : OUTPUT "Invalid choice".

Key Term

OTHERWISE

The last clause of a CASE statement. It runs when the variable matches none of the listed values, e.g. OTHERWISE : OUTPUT "Invalid choice". Without it, nothing happens if no value matches.

Fill in the Blanks

1. CASE OF Choice 1 : OUTPUT "Play" OTHERWISE : OUTPUT "Invalid choice"

Hint: Type the last clause that runs when none of the listed values match.

2. 1 : OUTPUT "Play" OTHERWISE : OUTPUT "Invalid choice" ENDCASE

Hint: Type the keyword that displays a message on the screen.

3. 2 : OUTPUT "Quit" OTHERWISE : OUTPUT "Invalid choice" ENDCASE

Hint: Type the keyword that closes the CASE statement after the last clause.

4. CASE OF Menu OTHERWISE : OUTPUT "Invalid choice" ENDCASE

Hint: Type the keyword that links CASE to the variable being tested.

5. 3 : OUTPUT "Exit" OTHERWISE : OUTPUT "Invalid choice" ENDCASE

Hint: Type the clause that is always written last and catches every other value.

Spot the Error

Question 1

A CASE OF Choice

B 1 OUTPUT "Start"

C OTHERWISE : OUTPUT "Error"

D ENDCASE

Line B — Each CASE clause needs a colon between the value and the statement. It should be 1 : OUTPUT "Start".

Question 2

A CASE Menu

B 1 : OUTPUT "Play"

C 2 : OUTPUT "Quit"

D OTHERWISE : OUTPUT "Error"

E ENDCASE

Line A — A CASE statement starts with CASE OF followed by the variable. OF is missing; it should be CASE OF Menu. Without it, the OTHERWISE clause has no valid CASE to belong to.

Question 3

A CASE OF Day

B 1 : OUTPUT "Mon"

C 2 : OUTPUT "Tue"

D OTHERWISE OUTPUT "Error"

E ENDCASE

Line D — OTHERWISE must be followed by a colon, just like the value clauses. It should be OTHERWISE : OUTPUT "Error".

Question 4

A CASE Grade OF

B "A" : OUTPUT "Top"

C "B" : OUTPUT "Good"

D OTHERWISE : OUTPUT "Error"

E ENDCASE

Line A — The keywords come first, then the variable: CASE OF Grade. The words are in the wrong order. Then OTHERWISE can catch any grade that is not A or B.

Question 5

A CASE OF Choice

B 1 : OUTPUT "Start"

C ELSE : OUTPUT "Error"

D ENDCASE

Line C — ELSE belongs to IF statements. The last CASE clause that runs when no value matches is OTHERWISE. It should be OTHERWISE : OUTPUT "Error".

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