Selection

Exam code: 2210

Written by: Ashika|Reviewed by: Caroline Carroll|Updated 2 July 2026

What is Selection?

Selection is when the flow of a program is changed, depending on a set of conditions
The outcome of this condition will then determine which lines or block of code is run next
Selection is used for validation, calculation and making sense of a user's choices
There are two ways to write selection statements:
- if... then... else...
- case...

If Statements

What is an If statement?

As If statements allow you to execute a set of instructions if a condition is true
They have the following syntax:

IF <condition>
THEN
<statement>
ENDIF
A detailed look at a Python IF statement:

if-else-if-else-statement-pseudocode-computer-science-revision-notes

Example

Concept	Pseudocode	Python
IF-THEN-ELSE	`IF Answer ← "Yes" THEN OUTPUT "Correct" ELSE OUTPUT "Wrong" ENDIF`	`if answer == "Yes": print("Correct") elif answer == "No": print("Wrong") else: print("Error")`

Nested Selection

What is nested selection?

Nested selection is a selection statement within a selection statement, e.g. an If inside of another If
Nested means to be 'stored inside the other'

Example

Pseudocode
`IF Player2Score > Player1Score THEN IF Player2Score > HighScore THEN OUTPUT Player2, " is champion and highest scorer" ELSE OUTPUT Player2, " is the new champion" ENDIF ELSE OUTPUT Player1, " is still the champion" IF Player1Score > HighScore THEN OUTPUT Player1, " is also the highest scorer" ENDIF ENDIF`

Pseudocode

IF Player2Score > Player1Score 
    THEN 
         IF Player2Score > HighScore 
             THEN 
                  OUTPUT Player2, " is champion and highest scorer" 
             ELSE 
                  OUTPUT Player2, " is the new champion" 
         ENDIF 
    ELSE 
         OUTPUT Player1, " is still the champion" 
         IF Player1Score > HighScore 
             THEN 
                  OUTPUT Player1, " is also the highest scorer" 
         ENDIF 
ENDIF

Python
`# Prompt the user to enter a number print("Enter a number: ") test_score = int(input()) # Outer statement to check if the test_score is above 40 if test_score > 40: # Inner statement to assign the result from the test if test_score > 70: result = "Distinction" elif test_score > 55: result = "Merit" else: result = "Pass" else: result = "Fail" # Output the result print(result)`

Python

# Prompt the user to enter a number
print("Enter a number: ")
test_score = int(input())

# Outer statement to check if the test_score is above 40
if test_score > 40:
    # Inner statement to assign the result from the test
    if test_score > 70:
        result = "Distinction"
    elif test_score > 55:
        result = "Merit"
    else:
        result = "Pass" 
else:
    result = "Fail"

# Output the result
print(result)

Case Statements

What is a case statement?

A case statement can mean less code but it only useful when comparing multiple values of the same variable
If statements are more flexible and are generally used more in languages such as Python
The format of a CASE statement is:
CASE OF <identifier>
<value 1> : <statement>
<value 2>: <statement>
....
OTHERWISE <statement>
ENDCASE

Concept	Pseudocode	Python
CASE	`INPUT Move CASE OF Move 'W' : Position ← Position - 10 'E' : Position ← Position + 10 'A' : Position ← Position - 1 'D' : Position ← Position + 1 OTHERWISE OUTPUT "Beep" ENDCASE`	`day = "Sat" match day: case "Sat": print("Saturday") case "Sun": print("Sunday") case _: print("Weekday")`

Concept

Pseudocode

Python

CASE

INPUT Move

CASE OF Move
    'W' : Position ← Position - 10
    'E' : Position ← Position + 10
    'A' : Position ← Position - 1
    'D' : Position ← Position + 1
    OTHERWISE 
        OUTPUT "Beep"
ENDCASE

day = "Sat"
match day:
    case "Sat":
        print("Saturday")
    case "Sun":
        print("Sunday")
    case _:
        print("Weekday")

Worked example

Write an algorithm using pseudocode that:

Inputs 3 numbers
Outputs the largest of the three numbers

[3]

Exemplar answer

Pseudocode
`INPUT A INPUT B INPUT C IF A >= B AND A >= C THEN OUTPUT A ELSE IF B >= A AND B >= C THEN OUTPUT B ELSE OUTPUT C ENDIF`

Python
`if A > B and A > C: print(A) elif B > C: print(B) else: print(C)`

What is Selection?

If Statements

If Statements

What is an If statement?

Example

Nested Selection

Nested Selection

What is nested selection?

Example

Case Statements

Case Statements

What is a case statement?

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