Selection (Cambridge (CIE) A Level Computer Science): Revision Note

Exam code: 9618

Written by: Robert Hampton

Reviewed by: James Woodhouse

Updated on 5 May 2025

Selection

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?

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

Pseudocode
`IF <condition> THEN <statement(s)> ENDIF`	`IF <condition> THEN <statement(s)> ELSE <statement(s)> ENDIF`
Without an ELSE clause	With an ELSE clause

Nested if statements

Nested if statements are an if statement within an if statement
Nested means to be 'stored inside the other'

Example code

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

If statements in different languages

Python	VB.net	Java
`weather = input("What is the weather like today? (sunny, rainy, snowy): ") if weather == "sunny": print("Don't forget your sunglasses!") elif weather == "rainy": print("Take an umbrella with you.") elif weather == "snowy": print("Wear warm clothes!") else: print("Not sure what to suggest for that kind of weather.")`	Module WeatherCheck Sub Main() Dim weather As String Console.Write("What is the weather like today? (sunny, rainy, snowy): ") weather = Console.ReadLine() If weather = "sunny" Then Console.WriteLine("Don't forget your sunglasses!") ElseIf weather = "rainy" Then Console.WriteLine("Take an umbrella with you.") ElseIf weather = "snowy" Then Console.WriteLine("Wear warm clothes!") Else Console.WriteLine("Not sure what to suggest for that kind of weather.") End If Console.ReadLine() ' Keeps the console open End Sub End Module	import java.util.Scanner; public class WeatherCheck { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String weather; System.out.print("What is the weather like today? (sunny, rainy, snowy): "); weather = scanner.nextLine(); if (weather.equals("sunny")) { System.out.println("Don't forget your sunglasses!"); } else if (weather.equals("rainy")) { System.out.println("Take an umbrella with you."); } else if (weather.equals("snowy")) { System.out.println("Wear warm clothes!"); } else { System.out.println("Not sure what to suggest for that kind of weather."); } scanner.close(); } }

Python

VB.net

Java

weather = input("What is the weather like today? (sunny, rainy, snowy): ")

if weather == "sunny":
    print("Don't forget your sunglasses!")
elif weather == "rainy":
    print("Take an umbrella with you.")
elif weather == "snowy":
    print("Wear warm clothes!")
else:
    print("Not sure what to suggest for that kind of weather.")

Module WeatherCheck
    Sub Main()
        Dim weather As String

        Console.Write("What is the weather like today? (sunny, rainy, snowy): ")
        weather = Console.ReadLine()

        If weather = "sunny" Then
            Console.WriteLine("Don't forget your sunglasses!")
        ElseIf weather = "rainy" Then
            Console.WriteLine("Take an umbrella with you.")
        ElseIf weather = "snowy" Then
            Console.WriteLine("Wear warm clothes!")
        Else
            Console.WriteLine("Not sure what to suggest for that kind of weather.")
        End If

        Console.ReadLine() ' Keeps the console open
    End Sub
End Module

import java.util.Scanner;

public class WeatherCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String weather;

        System.out.print("What is the weather like today? (sunny, rainy, snowy): ");
        weather = scanner.nextLine();

        if (weather.equals("sunny")) {
            System.out.println("Don't forget your sunglasses!");
        } else if (weather.equals("rainy")) {
            System.out.println("Take an umbrella with you.");
        } else if (weather.equals("snowy")) {
            System.out.println("Wear warm clothes!");
        } else {
            System.out.println("Not sure what to suggest for that kind of weather.");
        }

        scanner.close();
    }
}

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:

Pseudocode
`CASE of <identifier> <value 1> : <statement1> <statement2> ... <value 2> : <statement1> <statement2> ... ... ENDCASE`	`CASE of <identifier> <value 1> : <statement1> <statement2> ... <value 2> : <statement1> <statement2> ... OTHERWISE : <statement1> <statement2> ... ENDCASE`
	An `OTHERWISE` clause can be the last clause

Pseudocode

CASE of <identifier>
  <value 1> : <statement1>
              <statement2>
              ...
  <value 2> : <statement1>
              <statement2>
              ...
  ...
ENDCASE

CASE of <identifier>
  <value 1> : <statement1>
              <statement2>
              ...
  <value 2> : <statement1>
              <statement2>
              ...
  OTHERWISE : <statement1>
              <statement2>
              ...
ENDCASE

An OTHERWISE clause can be the last clause

Example code

DECLARE Direction : STRING

OUTPUT "Enter a direction (N, S, E, W):"
INPUT Direction

CASE OF Direction
    "N" : OUTPUT "You are heading North"
    "S" : OUTPUT "You are heading South"
    "E" : OUTPUT "You are heading East"
    "W" : OUTPUT "You are heading West"
    OTHERWISE : OUTPUT "Invalid direction entered"
ENDCASE

Case statements in different languages

Python	VB.net	Java
`weather = input("What is the weather like today? (sunny, rainy, snowy): ") match weather: case "sunny": print("Don't forget your sunglasses!") case "rainy": print("Take an umbrella with you.") case "snowy": print("Wear warm clothes!") case _: print("Not sure what to suggest for that kind of weather.")`	Module WeatherCheck Sub Main() Dim weather As String Console.Write("What is the weather like today? (sunny, rainy, snowy): ") weather = Console.ReadLine() Select Case weather Case "sunny" Console.WriteLine("Don't forget your sunglasses!") Case "rainy" Console.WriteLine("Take an umbrella with you.") Case "snowy" Console.WriteLine("Wear warm clothes!") Case Else Console.WriteLine("Not sure what to suggest for that kind of weather.") End Select Console.ReadLine() ' Keeps the console open End Sub End Module	import java.util.Scanner; public class WeatherCheck { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String weather; System.out.print("What is the weather like today? (sunny, rainy, snowy): "); weather = scanner.nextLine(); switch (weather) { case "sunny": System.out.println("Don't forget your sunglasses!"); break; case "rainy": System.out.println("Take an umbrella with you."); break; case "snowy": System.out.println("Wear warm clothes!"); break; default: System.out.println("Not sure what to suggest for that kind of weather."); break; } scanner.close(); } }

Python

VB.net

Java

weather = input("What is the weather like today? (sunny, rainy, snowy): ")

match weather:
    case "sunny":
        print("Don't forget your sunglasses!")
    case "rainy":
        print("Take an umbrella with you.")
    case "snowy":
        print("Wear warm clothes!")
    case _:
        print("Not sure what to suggest for that kind of weather.")

Module WeatherCheck
    Sub Main()
        Dim weather As String

        Console.Write("What is the weather like today? (sunny, rainy, snowy): ")
        weather = Console.ReadLine()

        Select Case weather
            Case "sunny"
                Console.WriteLine("Don't forget your sunglasses!")
            Case "rainy"
                Console.WriteLine("Take an umbrella with you.")
            Case "snowy"
                Console.WriteLine("Wear warm clothes!")
            Case Else
                Console.WriteLine("Not sure what to suggest for that kind of weather.")
        End Select

        Console.ReadLine() ' Keeps the console open
    End Sub
End Module

import java.util.Scanner;

public class WeatherCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String weather;

        System.out.print("What is the weather like today? (sunny, rainy, snowy): ");
        weather = scanner.nextLine();

        switch (weather) {
            case "sunny":
                System.out.println("Don't forget your sunglasses!");
                break;
            case "rainy":
                System.out.println("Take an umbrella with you.");
                break;
            case "snowy":
                System.out.println("Wear warm clothes!");
                break;
            default:
                System.out.println("Not sure what to suggest for that kind of weather.");
                break;
        }

        scanner.close();
    }
}

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Selection (Cambridge (CIE) A Level Computer Science): Revision Note

Selection

What is selection?

If statements

What is an if statement?

Nested if statements

Example code

If statements in different languages

Case statements

What is a case statement?

Example code

Case statements in different languages

You've read 0 of your 5 free revision notes this week

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

1. Information representation

Data Representation

Binary Prefixes

Number Systems

Binary Arithmetic

Uses of Number Systems

Character Encoding

Multimedia

Bitmap Images

Vector Graphics

Sound Representation

Compression

Compression

Compression Techniques

2. Communication

Networks & the Internet

Network Types

Network Models

Network Topologies

Cloud Computing

Transmission Media

Network Hardware

Ethernet

Bit Streaming

The Internet

IP Addressing

Locating Resources on the World Wide Web

3. Hardware

Computers & Components

System Components

Embedded Systems

Hardware Devices

Memory Types

Monitoring & Control

Logic Gates & Logic Circuits

Logic Gates

Logic Construction

4. Processor Fundamentals

Central Processing Unit (CPU) Architecture

System Architecture

Components of the CPU

System Performance

Ports & Interfaces

Fetch-Execute Cycle

Interrupts

Assembly Language

Assembly Language Basics

Assembly Process

Instruction Groups

Addressing Modes

Bit Manipulation

Bitwise Operations

5. System Software

Operating Systems

Operating System Fundamentals

Utility Software

Program Libraries

Language Translators

Translator Types

Development Tools

6. Security, privacy & data integrity

Data Security

Security Measures

Threats

Data Protection