choosing which statements to run, depending on a condition. IF and CASE are selection statements.

Number holds 8. What does IF Number > 10 THEN OUTPUT "Big" ELSE OUTPUT "Small" ENDIF output?

Small. 8 > 10 is false, so the ELSE part runs.

Which keyword ends an IF statement?

ENDIF. ENDCASE ends a CASE statement.

In a CASE statement, what is OTHERWISE for?

to say what happens when no value matches. It catches every value not listed.

an IF statement inside another IF statement. The inner decision depends on the outer one.

Selection: IF and CASE · Cambridge IGCSE Computer Science (9

In plain words

A program that does exactly the same thing every time is not much use. Selection lets it choose: test a condition, and run one set of statements or another depending on the answer.

5 things to know

Sequence means statements are carried out one after another, in order. Selection means choosing which statements to carry out.
IF Mark >= 50 THEN OUTPUT "Pass" ELSE OUTPUT "Fail" ENDIF. The statements after THEN run when the condition is true. Those after ELSE run when it is false.
The ELSE part can be left out if nothing needs to happen when the condition is false.
CASE OF tests one variable against several values. Each value has its own statement, and OTHERWISE covers anything that does not match. It ends with ENDCASE.
A nested IF is an IF statement inside another one. It is used when a second decision depends on the first.

Worked example

Age holds 15. What is output by: IF Age >= 18 THEN OUTPUT "Adult" ELSE IF Age >= 13 THEN OUTPUT "Teen" ELSE OUTPUT "Child" ENDIF ENDIF?

First condition: is 15 >= 18? No. So the ELSE part runs.
Second condition: is 15 >= 13? Yes. So "Teen" is output.
The final ELSE is skipped.

Tips and tricks

Every IF needs its ENDIF and every CASE OF needs its ENDCASE. Count them, especially when one is nested inside another.
Use CASE when one variable is compared with a list of values. Use IF for ranges, or when two different variables are tested.

6 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Selection: IF and CASE: 6 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is selection?
- repeating statements
- choosing which statements to run, depending on a condition (the answer)
- storing a list of values
- running statements in order
IF and CASE are selection statements.
Number holds 8. What does IF Number > 10 THEN OUTPUT "Big" ELSE OUTPUT "Small" ENDIF output?
- Big
- Small (the answer)
- nothing
- 8
8 > 10 is false, so the ELSE part runs.
Which keyword ends an IF statement?
- NEXT
- UNTIL
- ENDIF (the answer)
- ENDCASE
ENDCASE ends a CASE statement.
In a CASE statement, what is OTHERWISE for?
- to end the statement
- to say what happens when no value matches (the answer)
- to repeat the statement
- to declare a variable
It catches every value not listed.
What is a nested IF?
- an IF with no ELSE
- an IF statement inside another IF statement (the answer)
- two IF statements side by side
- an IF inside a comment
The inner decision depends on the outer one.
Score holds 50. What does IF Score >= 50 THEN OUTPUT "Pass" ELSE OUTPUT "Fail" ENDIF output?
- Pass (the answer)
- Fail
- nothing
- 50
50 >= 50 is true.

6 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

2 questions, 5 marks. Write your answers on paper, then check them.

Selection: IF and CASE

Cambridge IGCSE Computer Science (9–1) 0984 · 5 marks · papermunch.org

Name ______________________________ Date ______________

Write a pseudocode IF statement that outputs "Hot" if Temp is more than 30 and "Mild" if not.[3]
Show answerHide answer
IF Temp > 30 THEN OUTPUT "Hot" ELSE OUTPUT "Mild" ENDIF
I got this one
Explain when a CASE statement is more suitable than IF statements.[2]
Show answerHide answer
When a single variable has to be compared with several different values, each needing its own action. It is clearer than many separate IF statements.
I got this one

Answers: Selection: IF and CASE

1. IF Temp > 30 THEN OUTPUT "Hot" ELSE OUTPUT "Mild" ENDIF
2. When a single variable has to be compared with several different values, each needing its own action. It is clearer than many separate IF statements.