Skip to content

pseudocode.md

Latest commit

 

History

History
457 lines (331 loc) · 10.4 KB

pseudocode.md

File metadata and controls

457 lines (331 loc) · 10.4 KB
Raw

Cambridge Pseudocode Language Guide

This guide documents the pseudocode language supported by the compiler, based on Cambridge IGCSE Computer Science (0478/0984/2210) and Cambridge International AS & A Level Computer Science (9618).

General Style Conventions

  • Keywords are in UPPERCASE (e.g., IF, REPEAT, PROCEDURE)
  • Identifiers use PascalCase (e.g., NumberOfPlayers, StudentName)
  • Comments start with //
  • Indentation is recommended (4 spaces) but not enforced
  • The language is case-insensitive for keywords

Basic Data Types

Type Description Example Literals
INTEGER Whole number 5, -3
REAL Decimal number 4.7, 0.3, -4.0
CHAR Single character 'x', '@'
STRING Sequence of characters "Hello", ""
BOOLEAN Logical value TRUE, FALSE

Variables and Constants

Declaring Variables

DECLARE <identifier> : <data type>

Example:

DECLARE Counter : INTEGER
DECLARE TotalToPay : REAL
DECLARE GameOver : BOOLEAN
DECLARE StudentName : STRING

Declaring Constants

CONSTANT <identifier> <- <value>

Example:

CONSTANT HourlyRate <- 6.50
CONSTANT DefaultText <- "N/A"

Only literals can be used as constant values.

Assignment

Assignment uses the <- operator (or =):

<identifier> <- <value>

Example:

Counter <- 0
Counter <- Counter + 1
TotalToPay <- NumberOfHours * HourlyRate

Arrays

Declaring 1D Arrays

DECLARE <identifier> : ARRAY[<lower>:<upper>] OF <data type>

Example:

DECLARE StudentNames : ARRAY[1:30] OF STRING

Declaring 2D Arrays

DECLARE <identifier> : ARRAY[<lower1>:<upper1>, <lower2>:<upper2>] OF <data type>

Example:

DECLARE NoughtsAndCrosses : ARRAY[1:3, 1:3] OF CHAR

Using Arrays

StudentNames[1] <- "Ali"
NoughtsAndCrosses[2,3] <- 'X'
StudentNames[n+1] <- StudentNames[n]

Array Literals

A one-dimensional array can also be created directly from a list of values. Array literals use 1-based bounds, so this example creates Numbers[1] through Numbers[5]:

Numbers <- [1, 3, 8, 10, 12]
OUTPUT Numbers[1]

Input and Output

Input

INPUT <identifier>

Output

OUTPUT <value(s)>

Multiple values can be output in one statement, separated by commas. PRINT is also accepted as an alias for OUTPUT.

Example:

INPUT Answer
OUTPUT "You have ", Lives, " lives left"

Operators

Arithmetic Operators

Operator Operation Example
+ Addition 5 + 3
- Subtraction 5 - 3
* Multiplication 5 * 3
/ Division 10 / 3
^ Power 2 ^ 3

Integer Division

DIV returns the quotient (whole number part):

DIV(10, 3)    // returns 3
10 DIV 3      // also supported

MOD returns the remainder:

MOD(10, 3)    // returns 1
10 MOD 3      // also supported

Comparison Operators

Operator Meaning
= Equal to
<> Not equal to
< Less than
> Greater than
<= Less than or equal to
>= Greater than or equal to

Logical Operators

Operator Operation
AND Logical AND
OR Logical OR
NOT Logical NOT

String Concatenation

Use & to concatenate strings:

FullName <- FirstName & " " & LastName

Selection

IF Statement

IF <condition> THEN
    <statements>
ENDIF

IF-ELSE Statement

IF <condition> THEN
    <statements>
ELSE
    <statements>
ENDIF

IF-ELSEIF Statement

IF <condition> THEN
    <statements>
ELSEIF <condition> THEN
    <statements>
ELSE
    <statements>
ENDIF

CASE Statement

CASE OF <identifier>
    <value1> :
        <statement>
    <value2> :
        <statement>
    OTHERWISE:
        <statement>
ENDCASE

Example:

CASE OF Move
    'W' :
        Position <- Position - 10
    'S' :
        Position <- Position + 10
    OTHERWISE:
        OUTPUT "Invalid move"
ENDCASE

Iteration

Count-controlled Loop (FOR)

FOR <identifier> <- <value1> TO <value2>
    <statements>
NEXT <identifier>

With step:

FOR <identifier> <- <value1> TO <value2> STEP <increment>
    <statements>
NEXT <identifier>

Example:

FOR Counter <- 1 TO 10
    OUTPUT Counter
NEXT Counter

FOR Index <- 10 TO 1 STEP -1
    OUTPUT Index
NEXT Index

Post-condition Loop (REPEAT)

REPEAT
    <statements>
UNTIL <condition>

Executes at least once; tests condition after each iteration.

Pre-condition Loop (WHILE)

WHILE <condition> DO
    <statements>
ENDWHILE

Tests condition before each iteration; may not execute at all.

Procedures and Functions

Procedure Declaration

PROCEDURE <identifier>(<param1>:<datatype>, <param2>:<datatype>...)
    <statements>
ENDPROCEDURE

Calling Procedures

CALL <identifier>(value1, value2...)

Function Declaration

FUNCTION <identifier>(<param1>:<datatype>, <param2>:<datatype>...) RETURNS <data type>
    <statements>
    RETURN <value>
ENDFUNCTION

Calling Functions

Functions are normally called as part of expressions so their returned value can be used:

OUTPUT "Sum of squares = ", SumSquare(10, 20)

Example:

FUNCTION SumSquare(Number1:INTEGER, Number2:INTEGER) RETURNS INTEGER
    RETURN Number1 * Number1 + Number2 * Number2
ENDFUNCTION

OUTPUT SumSquare(3, 4)

When the returned value is intentionally not needed, CALL can execute the function and discard its result:

CALL SumSquare(3, 4)

File Handling

Files are simulated using browser localStorage. Each file is stored as a key-value pair.

Opening Files

OPENFILE <file identifier> FOR <file mode>

File modes:

  • READ - open for reading
  • WRITE - open for writing (creates new / overwrites existing)
  • APPEND - open for appending to existing content

Reading from Files

READFILE <file identifier>, <variable>

Reads one line at a time into the variable.

Writing to Files

WRITEFILE <file identifier>, <variable>

Writes a line to the file.

Closing Files

CLOSEFILE <file identifier>

Always close files when done. Written data is saved to localStorage on close.

Checking End of File

EOF(<file identifier>)

Returns TRUE if there are no more lines to read.

Example

// Writing to a file
OPENFILE "data.txt" FOR WRITE
WRITEFILE "data.txt", "Hello"
WRITEFILE "data.txt", "World"
CLOSEFILE "data.txt"

// Reading from a file
DECLARE LineOfText : STRING
OPENFILE "data.txt" FOR READ
WHILE NOT EOF("data.txt") DO
    READFILE "data.txt", LineOfText
    OUTPUT LineOfText
ENDWHILE
CLOSEFILE "data.txt"

Cambridge International AS & A Level Computer Science (9618)

Cambridge International AS & A Level Computer Science (9618) develops computational thinking and programming skills for higher education computer science courses and twenty-first century digital employers. The 9618 pseudocode guide extends the IGCSE subset with:

  • TYPE definitions for records, enumerated types, pointer types, and SET OF
  • DEFINE for set values
  • DATE values written as dd/mm/yyyy
  • BYREF and BYVAL parameters
  • CASE ranges and multi-value labels
  • Random-access files with OPENFILE ... FOR RANDOM, SEEK, GETRECORD, and PUTRECORD
  • Object-oriented syntax with CLASS, ENDCLASS, INHERITS, PUBLIC, PRIVATE, NEW, and SUPER

The syllabus year refers to the year in which the examination will be taken. Cambridge 9618 materials include the 2024-2025 syllabus and update, the 2026 syllabus and update, the 2026 Pseudocode Guide for Teachers, the 2027-2029 syllabus and update, the 2027-2029 Pseudocode Guide, and the 2023-2025 AS and A Level grade descriptions.

String Operations

Function Description Example
LENGTH(s) Returns the length of a string LENGTH("Hello") returns 5
LCASE(s) Converts to lowercase LCASE("Hello") returns "hello"
UCASE(s) Converts to uppercase UCASE("Hello") returns "HELLO"
SUBSTRING(s, start, length) Extracts a substring (1-based) SUBSTRING("Hello", 1, 3) returns "Hel"
LEFT(s, length) Returns leftmost characters LEFT("Hello", 3) returns "Hel"
RIGHT(s, length) Returns rightmost characters RIGHT("Hello", 3) returns "llo"
MID(s, start, length) Same as SUBSTRING MID("Hello", 2, 3) returns "ell"

Other Library Routines

Function Description Example
ROUND(n, places) Rounds to specified decimal places ROUND(3.14159, 2) returns 3.14
RANDOM() Returns a random number between 0 and 1 RANDOM()
INT(n) Truncates to integer INT(3.7) returns 3
DIV(a, b) Integer division DIV(10, 3) returns 3
MOD(a, b) Remainder MOD(10, 3) returns 1
ASC(c) Returns the ASCII code of a character ASC('A') returns 65
CHR(n) Returns the character for an ASCII code CHR(65) returns 'A'
NUM_TO_STRING(n) Converts number to string NUM_TO_STRING(42) returns "42"
STRING_TO_NUM(s) Converts string to number STRING_TO_NUM("42") returns 42
IS_NUM(s) Checks if a string is numeric IS_NUM("42") returns TRUE
EOF(f) Checks if end of file reached EOF("data.txt")