Programming

Programming
Programming is the heart of computer science. This section covers the fundamental concepts you need to write, understand, and debug code effectively. From basic data types to complex procedures, you'll master the building blocks of computational thinking required for your IGCSE exam.
Data Types & Variables
Every program needs to store and manipulate data. Understanding data types and how to declare variables and constants is the foundation of programming.
Data Types
Data types classify the kind of values a variable can hold. Choosing the correct data type is crucial for efficient memory usage and preventing errors.

INTEGER: Whole numbers (e.g., 5, -10, 1000).

CHAR: A single character (e.g., 'a', 'Z', '7', '$').

STRING: A sequence of characters (e.g., "Hello World", "IGCSE").

REAL: Numbers with decimal points (e.g., 3.14, -0.5, 99.99).

BOOLEAN: Represents truth values, either TRUE or FALSE.

Pseudocode

DECLARE age : INTEGER
DECLARE price : REAL
DECLARE initial : CHAR
DECLARE name : STRING
DECLARE isAdmin : BOOLEAN


Visual Basic

Dim age As Integer
Dim price As Single
Dim initial As Char
Dim name As String
Dim isAdmin As Boolean
Variables
Variables are named storage locations in memory used to hold data that can change during the program's execution. They allow programs to be dynamic and respond to different inputs or states.

Pseudocode

DECLARE score : INTEGER
score ← 0
score ← score + 10
OUTPUT score // Outputs 10


Visual Basic

Dim score As Integer
score = 0
score = score + 10
Console.WriteLine(score) ' Outputs 10
Constants
Constants are named storage locations whose values cannot be changed once they have been defined. They are used for values that remain fixed throughout the program, improving readability and maintainability.

Pseudocode

CONSTANT PI = 3.14159
CONSTANT MAX_USERS = 100


Visual Basic

Const PI As Double = 3.14159
Const MAX_USERS As Integer = 100
Declaration Syntax
Declaring a variable or constant involves giving it a name and specifying its data type. This reserves the necessary memory space and helps the compiler or interpreter understand how to handle the stored value.

Pseudocode

// Variable Declaration
DECLARE variableName : DataType

// Constant Declaration
CONSTANT CONSTANT_NAME = value


Visual Basic

' Variable Declaration
Dim variableName As DataType

' Constant Declaration
Const CONSTANT_NAME As DataType = value
Input/Output Operations
Input operations allow programs to receive data from users or external sources, while output operations display results or information. These operations are fundamental for user interaction and conveying program status.

Pseudocode

DECLARE userName : STRING
OUTPUT "Enter your name: "
INPUT userName
OUTPUT "Hello, " & userName


Visual Basic

Dim userName As String
Console.Write("Enter your name: ")
userName = Console.ReadLine()
Console.WriteLine("Hello, " & userName)
Operators & Expressions
Operators allow you to perform calculations, make comparisons, and combine conditions. Mastering these is essential for writing effective algorithms.
Operators are fundamental building blocks in programming. Click on each section below to explore different types of operators with detailed examples.
Arithmetic Operators
Arithmetic operators perform mathematical calculations on numerical values.

Common Operators

+ → Addition

- → Subtraction

* → Multiplication

/ → Division (real number result)

DIV → Integer division (drops decimals)

MOD → Remainder after division

Pseudocode

result ← 5 + 3
result ← 10 - 4
result ← 6 * 2
result ← 20 / 4
result ← 17 DIV 5  // result = 3
result ← 17 MOD 5  // result = 2

Visual Basic

result = 5 + 3
result = 10 - 4
result = 6 * 2
result = 20 / 4
result = 17 \ 5  'integer division
result = 17 Mod 5  'remainder
Relational Operators
Relational operators compare two values.

Operators

> → greater than

< → less than

>= → greater than or equal to

<= → less than or equal to

= → equal to

<> → not equal to

Pseudocode

isGreater ← (age > 18)
isEqual ← (score = 100)
isDifferent ← (name <> "Alice")

Visual Basic

isGreater = (age > 18)
isEqual = (score = 100)
isDifferent = (name <> "Alice")
Logical Operators
Logical operators join or modify Boolean expressions.

Operators

AND → both conditions must be TRUE

OR → at least one condition is TRUE

NOT → reverses TRUE/FALSE

Pseudocode

canVote ← (age >= 18) AND (isCitizen = TRUE)
needsRetake ← (mark < 50) OR (attendance < 80)
isNotAdmin ← NOT isAdmin

Visual Basic

canVote = (age >= 18) And (isCitizen = True)
needsRetake = (mark < 50) Or (attendance < 80)
isNotAdmin = Not isAdmin
Library Routines (from syllabus)
Only the routines used in the 0478 syllabus:

ROUND(x)

RANDOM (returns a random number)

DIV and MOD already shown above

Pseudocode

value ← ROUND(3.67)  // value = 4
number ← RANDOM  // returns a random number

Visual Basic

value = Math.Round(3.67)
number = Rnd()  'returns random value
Selection Structures
Programs need to make decisions. Selection structures allow your code to choose different paths based on conditions, making programs intelligent and responsive.
IF (Single Condition)
A single condition IF statement executes a block of code only if the specified condition is true. If the condition is false, the code block is skipped, and the program continues after the END IF.

Pseudocode

IF age > 18 THEN
    OUTPUT "Adult"
END IF

Visual Basic

If age > 18 Then
    Console.WriteLine("Adult")
End If
IF / ELSE (Two-Way Selection)
IF / ELSE statements provide two possible paths of execution. If the condition is true, one block of code is executed; otherwise, the code in the ELSE block is executed.

Pseudocode

IF score >= 50 THEN
    OUTPUT "Pass"
ELSE
    OUTPUT "Fail"
END IF

Visual Basic

If score >= 50 Then
    Console.WriteLine("Pass")
Else
    Console.WriteLine("Fail")
End If
IF / ELSE IF / ELSE (Multi-Way Selection)
For scenarios requiring more than two outcomes, IF / ELSE IF / ELSE structures allow for multiple conditions to be checked sequentially, leading to different execution paths.

Pseudocode

IF mark >= 75 THEN
    OUTPUT "Distinction"
ELSE IF mark >= 60 THEN
    OUTPUT "Merit"
ELSE
    OUTPUT "Pass"
END IF

Visual Basic

If mark >= 75 Then
    Console.WriteLine("Distinction")
ElseIf mark >= 60 Then
    Console.WriteLine("Merit")
Else
    Console.WriteLine("Pass")
End If
CASE Statements
CASE statements, also known as SELECT CASE or SWITCH, provide a structured way to handle multiple possible outcomes based on the value of a single variable or expression, offering a cleaner alternative to complex IF / ELSE IF chains.

Pseudocode

CASE OF day
    WHEN "Mon": OUTPUT "Start of week"
    WHEN "Fri": OUTPUT "End of week"
    OTHERWISE: OUTPUT "Mid-week"
END CASE

Visual Basic

Select Case day
    Case "Mon"
        Console.WriteLine("Start of week")
    Case "Fri"
        Console.WriteLine("End of week")
    Case Else
        Console.WriteLine("Mid-week")
End Select
Boolean Conditions
Boolean conditions are expressions that evaluate to either TRUE or FALSE. They are essential for controlling the flow of selection structures, allowing programs to make decisions based on logical evaluations.

Pseudocode

isRaining ← TRUE
isCold ← FALSE
IF isRaining AND isCold THEN
    OUTPUT "Stay inside"
ELSE IF isRaining OR isCold THEN
    OUTPUT "Wear a jacket"
ELSE
    OUTPUT "Enjoy outside"
END IF

Visual Basic

Dim isRaining As Boolean = True
Dim isCold As Boolean = False
If isRaining And isCold Then
    Console.WriteLine("Stay inside")
ElseIf isRaining Or isCold Then
    Console.WriteLine("Wear a jacket")
Else
    Console.WriteLine("Enjoy outside")
End If
Iteration Structures (Loops)
Loops allow code to repeat, making programs efficient and powerful. Understanding when to use each type of loop is crucial for algorithm design.
FOR Loops (Count-Controlled)
Repeats a fixed number of times.

Can also use STEP for custom increments (e.g., FOR i ← 1 TO 10 STEP 2)
WHILE Loops (Pre-Condition)
Checks condition BEFORE executing. May not execute at all.

Use when you don't know how many iterations needed.
REPEAT...UNTIL Loops (Post-Condition)
Checks condition AFTER executing. Always runs at least once.

Useful for input validation.
Nested Loops
Loops inside loops. Common for 2D arrays. Inner loop completes fully for each iteration of outer loop.
Infinite Loops
Occur when loop condition never becomes false. Always ensure your loop will eventually terminate!
Choosing the Right Loop
Known iterations? Use FOR

Unknown iterations, may not run? Use WHILE

Unknown iterations, must run once? Use REPEAT...UNTIL
Pseudocode
// FOR Loop Example
FOR i ← 1 TO 5
    OUTPUT "Hello, iteration " & i
NEXT i

// WHILE Loop Example
DECLARE count : INTEGER
count ← 1
WHILE count <= 3
    OUTPUT "Counting: " & count
    count ← count + 1
END WHILE

// REPEAT...UNTIL Loop Example
DECLARE userInput : INTEGER
REPEAT
    OUTPUT "Enter a number greater than 0: "
    INPUT userInput
UNTIL userInput > 0
OUTPUT "Valid number entered: " & userInput
VB Code
' FOR Loop Example
For i As Integer = 1 To 5
    Console.WriteLine("Hello, iteration " & i.ToString())
Next

' WHILE Loop Example
Dim count As Integer = 1
While count <= 3
    Console.WriteLine("Counting: " & count.ToString())
    count += 1
End While

' DO WHILE Loop Example (pre-condition)
Dim num As Integer = 1
Do While num <= 3
    Console.WriteLine("Counting (Do While): " & num.ToString())
    num += 1
Loop

' DO...LOOP UNTIL Example (post-condition)
Dim userInput As Integer
Do
    Console.Write("Enter a number greater than 0: ")
    userInput = CInt(Console.ReadLine())
Loop Until userInput > 0
Console.WriteLine("Valid number entered: " & userInput.ToString())
Arrays
Arrays are fixed-length structures that store multiple values of the same data type. They're essential for handling collections of related data efficiently.
1D Arrays
Linear collection of same data type, accessed by single index

Index typically starts at 0 or 1

Example: scores[1], scores[5]
2D Arrays
Grid structure with rows and columns, accessed by two indices

Perfect for tables, game boards, matrices

Example: grid[2,3]
Array Declaration
Must declare size before use

Syntax: DECLARE arrayName : ARRAY[lower:upper] OF datatype

Example: DECLARE scores : ARRAY[1:10] OF INTEGER
Array Operations
Access elements using index in square brackets

Use loops to process all elements

Can store in variables: value ← scores[3]
Using Arrays with Loops
FOR loops are ideal for processing arrays

Can iterate through all elements

Useful for totalling, counting, searching
Pseudocode
VB Code
String Handling
String operations allow you to manipulate text data. Understanding these operations is essential for processing user input and formatting output.
LENGTH Function
Returns the number of characters in a string

Syntax: LENGTH(string)

Example: LENGTH("Hello") returns 5
SUBSTRING Function
Extracts a portion of a string

Syntax: SUBSTRING(string, start, length)

Example: SUBSTRING("Hello", 1, 3) returns "Hel"
UCASE Function
Converts all characters to uppercase

Syntax: UCASE(string)

Example: UCASE("hello") returns "HELLO"
LCASE Function
Converts all characters to lowercase

Syntax: LCASE(string)

Example: LCASE("HELLO") returns "hello"
String Indexing
First character can be position 0 or 1 (check your exam board)

Position matters for SUBSTRING operations

Cambridge IGCSE typically uses 1 as first position
Exam Tips
String operations return NEW values, don't modify original

Remember to check if indexing starts at 0 or 1

Can combine string operations together
Pseudocode
VB Code
Procedures & Functions
Breaking code into reusable blocks makes programs easier to write, test, and maintain. Understanding scope and parameters is key to modular programming.
Procedures
Named blocks of code that perform a task. Don't return a value:
Called using: CALL printMessage()
Functions
Named blocks that perform a task AND return a value:
Called in expressions: result ← square(5)
Parameters
Values passed into procedures/functions. Can have up to 2 parameters in IGCSE:
Local Variables
Declared inside a procedure/function. Only accessible within that block. Destroyed when block ends.
Global Variables
Declared outside all procedures/functions. Accessible throughout entire program. Use sparingly!
Benefits of Modular Code
Reusability: Write once, use many times
Testing: Test each module independently
Readability: Clear structure and purpose
Maintenance: Fix bugs in one place
Pseudocode
// Procedure with parameters and a function that returns a value

PROCEDURE Greet(name : STRING, age : INTEGER)
    OUTPUT "Hello ", name, ", you are ", age, " years old."
ENDPROCEDURE

FUNCTION Square(x : INTEGER) RETURNS INTEGER
    RETURN x * x
ENDFUNCTION

// Main program
DECLARE username : STRING
DECLARE userAge  : INTEGER
DECLARE result   : INTEGER

INPUT username
INPUT userAge

CALL Greet(username, userAge)

result ← Square(5)
OUTPUT "5 squared is ", result
VB Code
' Procedure with parameters and a function that returns a value

Module Program
    Sub Main()
        Dim username As String
        Dim userAge As Integer
        Dim result As Integer
        
        Console.Write("Enter your name: ")
        username = Console.ReadLine()
        
        Console.Write("Enter your age: ")
        userAge = CInt(Console.ReadLine())
        
        Greet(username, userAge)
        
        result = Square(5)
        Console.WriteLine("5 squared is {0}", result)
    End Sub
    
    Sub Greet(name As String, age As Integer)
        Console.WriteLine("Hello {0}, you are {1} years old.", name, age)
    Zend Sub
    
    Function Square(x As Integer) As Integer
        Return x * x
    End Function
End Module
File Handling & Pseudocode
Efficiently managing files and writing clear algorithms are fundamental skills in computer science. This section outlines key file operations and the pseudocode conventions you'll use in exams.
File Operations & Modes
OPENFILE: Opens a file for reading or writing.
READFILE: Reads data from an open file.
WRITEFILE: Writes data to an open file.
CLOSEFILE: Closes an open file, saving changes.
File Modes:
READ: Opens a file to read its contents.
WRITE: Opens a file to write to it (overwriting existing content or creating a new file).
Pseudocode Conventions
Pseudocode is used to describe algorithms in a structured, language-agnostic way, focusing on logic rather than specific syntax. In exams, adhere to the conventions provided in your syllabus to ensure clarity and consistency.
Key Pseudocode Commands
DECLARE: Declares a variable and its data type.
INPUT: Obtains input from the user.
OUTPUT: Displays output to the user.
IF...THEN...ELSE...ENDIF: Conditional execution.
FOR...NEXT: Loops a fixed number of times.
WHILE...DO...ENDWHILE: Loops as long as a condition is true, condition checked at start.
REPEAT...UNTIL: Loops until a condition is true, condition checked at end.
CASE OF...ENDCASE: Multi-way selection based on a variable's value.
Important Exam Note (Paper 2)
In Paper 2, you are generally expected to write solutions in pseudocode. The only exception is the 15-mark scenario question, for which you may use Python, Visual Basic, or Java to demonstrate your programming skills.
Pseudocode
// Read all names from a file and display them

DECLARE fileName : STRING
DECLARE name : STRING

fileName ← "students.txt"

OPENFILE fileName FOR READ

WHILE NOT EOF(fileName) DO
    READFILE fileName, name
    OUTPUT name
ENDWHILE

CLOSEFILE fileName
VB Code
' Read all names from a file and display them

Imports System.IO

Module Program
    Sub Main()
        Dim fileName As String = "students.txt"
        Dim line As String
        
        If File.Exists(fileName) Then
            Dim reader As New StreamReader(fileName)
            
            line = reader.ReadLine()
            While line IsNot Nothing
                Console.WriteLine(line)
                line = reader.ReadLine()
            End While
            
            reader.Close()
        Else
            Console.WriteLine("File not found.")
        End If
    End Sub
End Module
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