Mai's Lesson

Topic 8 · Programming

Selection with IF and CASE

Make decisions with IF, ELSE, nested IF statements, and CASE OF, using comparison and Boolean operators.

Lesson 2 of 7Syllabus 8.1updated October 31, 2026

IF ... THEN ... ELSE

Selection lets a program choose which statements to run. An IF statement checks a condition. If it is TRUE, the THEN block runs. If it is FALSE, the optional ELSE block runs instead.

Pseudocode
DECLARE Mark : INTEGER
INPUT Mark
IF Mark >= 50
  THEN
    OUTPUT "Pass"
  ELSE
    OUTPUT "Try again"
ENDIF
Which path runs?
MarkMark >= 50OUTPUT
72TRUEPass
50TRUEPass
49FALSETry again
0FALSETry again
Step 1 / 4
50 is the boundary: >= includes it, > would not.

Comparison operators

Conditions are built from comparisons, which always give TRUE or FALSE:

OperatorMeaningExample that is TRUE
=equal to5 = 5
<>not equal to5 <> 3
<less than3 < 5
<=less than or equal to5 <= 5
>greater than7 > 2
>=greater than or equal to7 >= 7

AND, OR, NOT

Boolean operators combine conditions. AND is TRUE only if both sides are TRUE. OR is TRUE if at least one side is TRUE. NOT flips TRUE and FALSE.

Pseudocode
DECLARE Age : INTEGER
DECLARE Ticket : STRING
INPUT Age
INPUT Ticket
IF Age >= 12 AND Ticket = "Y"
  THEN
    OUTPUT "Enjoy the film"
  ELSE
    OUTPUT "Sorry, you cannot go in"
ENDIF

Nested IF

An IF can sit inside the THEN or ELSE block of another IF. The inner condition is only checked when the program reaches the branch that contains it: here, only when Mark >= 70 is FALSE. Indent each level so you can see which ENDIF closes which IF.

Pseudocode
DECLARE Mark : INTEGER
INPUT Mark
IF Mark >= 70
  THEN
    OUTPUT "Grade A"
  ELSE
    IF Mark >= 50
      THEN
        OUTPUT "Grade B"
      ELSE
        OUTPUT "Grade C"
    ENDIF
ENDIF

CASE OF

When one variable is compared against several fixed values, CASE OF is shorter and clearer than many nested IFs. OTHERWISE catches every value not listed.

Pseudocode
DECLARE Choice : INTEGER
OUTPUT "1 Play  2 Settings  3 Quit"
INPUT Choice
CASE OF Choice
    1 : OUTPUT "Starting game"
    2 : OUTPUT "Opening settings"
    3 : OUTPUT "Goodbye"
    OTHERWISE : OUTPUT "Invalid choice"
ENDCASE

Key terms

Selection
Choosing which statements to run based on a condition.
Condition
An expression that evaluates to TRUE or FALSE.
Nested statement
A selection or loop placed inside another one.
CASE
Selection that compares one value against a list of options.

Check yourself

What is output when Mark is 50 in the nested IF example?Show answer

Grade B. The first test (>= 70) is FALSE, the second (>= 50) is TRUE.

Is NOT (5 > 3) OR 2 = 2 TRUE or FALSE?Show answer

NOT TRUE is FALSE, 2 = 2 is TRUE, and FALSE OR TRUE is TRUE.

When is CASE a better choice than IF?Show answer

When a single variable is compared against several specific values, such as a menu choice.

Practise this skill

Use what you learned in a question, then run your answer in the studio editor.

Selection
Open the studio editor PracticeOpen manual