Pseudocode Guide

This guide follows the official Cambridge IGCSE™ Computer Science (0478) syllabus for exams in 2026-2028. Mastering pseudocode is essential for success in Paper 2.

1. General Style

Pseudocode is designed to be readable and consistent. In your exam, it will appear in a fixed-width font (like Courier New).

Indentation

Indentation is used to show which statements belong together (e.g., inside a loop or an IF statement).

Standard indentation is four spaces.
THEN and ELSE clauses are only indented by two spaces.

Case and Identifiers

Keywords are always in UPPER CASE (e.g., IF, WHILE, PROCEDURE).
Identifiers (names for variables, constants, etc.) use PascalCase (e.g., TotalToPay, StudentName).
Identifiers must start with a capital letter and can only contain letters and digits (no underscores).

Comments

Use two forward slashes // to add notes to your code.

// This is a single line comment
Counter ← 0 // You can also add comments at the end of a line

2. Variables and Data Types

Data Types

IGCSE Computer Science uses five basic data types:

INTEGER: Whole numbers (e.g., 5, -10).
REAL: Numbers with fractional parts (e.g., 3.14, -0.5).
CHAR: A single character (e.g., 'A', '@').
STRING: A sequence of characters (e.g., "Hello World", "").
BOOLEAN: Logical values TRUE or FALSE.

Declarations

Always declare your variables before using them.

DECLARE Counter : INTEGER
DECLARE AverageScore : REAL
DECLARE IsFound : BOOLEAN

Constants

Use constants for values that do not change. This makes your code easier to maintain.

CONSTANT Pi ← 3.14159
CONSTANT MaxStudents ← 30

3. Basic Operations

Assignment

Use the left arrow ← to assign a value to a variable.

Total ← 0
Name ← "Alex"

Input and Output

INPUT: Gets a value from the user.
OUTPUT: Displays information on the screen.

OUTPUT "Please enter your name:"
INPUT UserName
OUTPUT "Hello, ", UserName

Arithmetic Operators

+ (Addition)
- (Subtraction)
* (Multiplication)
/ (Division)
^ (Power of)
DIV(x, y): Integer division (returns the whole number part).
MOD(x, y): Modulus (returns the remainder).

Result ← DIV(10, 3) // Result is 3
Remainder ← MOD(10, 3) // Remainder is 1

4. String Handling

String handling allows you to manipulate text. Positions in a string generally start at 1.

LENGTH(String): Returns the number of characters.
LCASE(String): Converts to lower case.
UCASE(String): Converts to upper case.
SUBSTRING(String, Start, Length): Extracts a part of the string.

MyText ← "Computer Science"
LengthText ← LENGTH(MyText) // returns 16
ShortText ← SUBSTRING(MyText, 1, 8) // returns "Computer"

5. Selection (Decision Making)

IF Statements

Used to execute code only if a condition is true.

IF Score >= 50
THEN
  OUTPUT "Pass"
ELSE
  OUTPUT "Fail"
ENDIF

CASE Statements

Used when you have multiple specific values to check.

CASE OF Grade
  'A' : OUTPUT "Excellent"
  'B' : OUTPUT "Good"
  'C' : OUTPUT "Satisfactory"
  OTHERWISE OUTPUT "Improvement needed"
ENDCASE

6. Iteration (Loops)

FOR Loops (Count-controlled)

Use when you know exactly how many times the loop should run.

FOR i ← 1 TO 10
  OUTPUT i
NEXT i

// Using a STEP
FOR j ← 10 TO 0 STEP -2
  OUTPUT j
NEXT j

WHILE Loops (Pre-condition)

Runs while a condition is true. The condition is checked before the loop runs.

WHILE Counter < 10 DO
  Counter ← Counter + 1
ENDWHILE

REPEAT UNTIL Loops (Post-condition)

Runs until a condition is true. The loop always runs at least once.

REPEAT
  OUTPUT "Enter a positive number:"
  INPUT Number
UNTIL Number > 0

7. Arrays

1D Arrays

DECLARE StudentNames : ARRAY[1:30] OF STRING
StudentNames[1] ← "Ali"

2D Arrays

DECLARE Grid : ARRAY[1:3, 1:3] OF CHAR
Grid[2, 3] ← 'X'

8. Procedures and Functions

Procedures

A block of code that performs a task but does not return a value.

PROCEDURE WelcomeUser(Name : STRING)
  OUTPUT "Welcome, ", Name
ENDPROCEDURE

// Calling a procedure
CALL WelcomeUser("Sam")

Functions

A block of code that performs a task and returns a single value.

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

// Using a function in an expression
Area ← Square(SideLength)

9. File Handling

Files allow you to store data permanently.

OPENFILE <filename> FOR <mode> (Modes: READ, WRITE)
READFILE <filename>, <variable>
WRITEFILE <filename>, <variable>
CLOSEFILE <filename>

OPENFILE "Scores.txt" FOR WRITE
WRITEFILE "Scores.txt", PlayerScore
CLOSEFILE "Scores.txt"

10. Library Routines

Common built-in tools:

ROUND(Value, Places): Rounds to specified decimal places.
RANDOM(): Returns a random number between 0 and 1.