Computer science

• Contents

  • Introduction
  • How should teachers use this guide?
  • Pseudocode in examined components
  • Font style and size
  • Indentation
  • Case and italics
  • Lines and numbering
  • Comments
  • Variables, constants and data types
  • Atomic type names
  • Literals
  • Identifiers
  • Assignments
  • Arrays
  • Declaring arrays
  • Using arrays
  • Common operations
  • Input and output
  • Arithmetic operations
  • Logic operators
  • Selection
  • IF statements
  • CASE statements
  • Iteration
  • Count-controlled (FOR) loops
  • Post-condition (REPEAT UNTIL) loops
• Cambridge International Examinations retains the copyright on all its publications
• Registered Centres are permitted to copy material from this booklet for their own internal use
• Centres cannot photocopy material acknowledged to a third party even for internal use within a Centre
• Version 2
• Types of loops

  • Count-controlled (FOR) loops
  • Post-condition (REPEAT UNTIL) loops
  • Pre-condition (WHILE) loops
• Index of symbols and keywords

  • Font style and size
  • Indentation
  • Case and italics
  • Lines and numbering
• Teachers should follow the guide in their teaching to help learners understand pseudocode presented in examination papers and pre-release materials more easily
• Using a recommended style in pseudocode will enable candidates to communicate their solutions more effectively to the Examiner
• Learners are not required to follow the guide in their examination answers or any other material presented for assessment
• Pseudocode is not a programming language with a defined, mandatory syntax
• Candidates will be given credit for pseudocode based on the logic of the solution presented
• Pseudocode will be presented in a monospaced (fixed-width) font such as Courier New with consistent font size
• Lines in pseudocode are indented by four spaces, with continuation lines indented by two spaces if needed
• Keywords in pseudocode are in uppercase, identifiers are in mixed case, and meta-variables are enclosed in angled brackets
• Descriptions in pseudocode are written in italics
• Line numbers in pseudocode are presented to the left with sufficient space to indicate they are not part of the statements
• Line numbers are consecutive unless skipped to indicate missing code
• Each line representing a statement in pseudocode is numbered, even if a statement runs over one line
• Comments in pseudocode are preceded by two forward slashes // and continue until the end of the line. For multi-line comments, each line is preceded by //
• Variables, constants, and data types are essential in pseudocode
• Atomic type names

  • INTEGER: A whole number
  • REAL: A number capable of containing a fractional part
  • CHAR: A single character
  • STRING: A sequence of zero or more characters
  • BOOLEAN: The logical values TRUE and FALSE
• Literals of data types

  • Integers: Written as normal in the denary system, e.g. 5, -3
  • Real: Always written with at least one digit on either side of the decimal point, zeros being added if necessary, e.g. 4.7, 0.3, -4.0, 0.0
  • Char: A single character delimited by single quotes, e.g. 'x', 'C', '@'
  • String: Delimited by double quotes. A string may contain no characters (i.e. the empty string) e.g. "This is a string", ""
  • Boolean: TRUE, FALSE
• Identifiers

  Names given to variables, constants, procedures, and functions. Must be in mix case, start with a letter, and can only contain letters (A-Z, a-z) and digits (0-9)
• Assignments


  The assignment operator is ←. Assignments should be made in the format: <identifier> ← <value>
• Declaring arrays

  Arrays are fixed-length structures of elements of identical data type, accessible by consecutive index numbers. Lower bound should be explicitly stated. One-dimensional arrays are declared as DECLARE <identifier> : ARRAY[<l>:<n>] OF <data type>
• Using arrays

  In main pseudocode statements, only one index value is used for each dimension in the square brackets
• Allowed array assignment

  • mes[n+1] ← StudentNames[n]
  • SavedGame ← NoughtsAndCrosses
• Statement should not refer to a group of array elements individually
• Loop structure for assigning array elements individually

  1. FOR Index = 1 TO 30

  2. StudentNames[Index] ← ""

  3. NEXT Index
• Values are input using the INPUT command
• Values are output using the OUTPUT command
• Input and Output statements

  • INPUT Answer
  • OUTPUT Score
  • OUTPUT "You have ", Lives, " lives left"
• Standard arithmetic operator symbols are used: + (Addition), - (Subtraction), * (Multiplication), / (Division)
• Resulting value of division operation should be of data type REAL, even if operands are integers
• Logic operators used are AND, OR, and NOT
• IF statements may or may not have an ELSE clause
• IF statement without ELSE clause

  IF <condition> THEN <statements> ENDIF
• IF statement with ELSE clause

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

  IF ChallengerScore > ChampionScore THEN IF ChallengerScore > HighestScore THEN OUTPUT ChallengerName, " is champion and highest scorer" ELSE OUTPUT Player1Name, " is the new champion" ENDIF ELSE OUTPUT ChampionName, " is still the champion" IF ChampionScore > HighestScore THEN OUTPUT ChampionName, " is also the highest scorer" ENDIF ENDIF