O LevelComputer ScienceCambridge (CIE)Revision Notes8. ProgrammingProgramming ConceptsVariables & Constants

Variables & Constants (Cambridge (CIE) O Level Computer Science)

Revision Note

Robert Hampton

Expertise

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Variables & Constants

What is a variable?

  • A variable is an identifier that can change in the lifetime of a program

  • Identifiers should be:

    • In mixed case (Pascal case)

    • Only contain letters (A-Z, a-z)

    • Only contain digits (0-9)

    • Start with a capital letter and not a digit

  • A variable can be associated a datatype when it is declared

  • When a variable is declared, memory is allocated based on the data type indicated

Pseudocode

DECLARE <identifier> : <datatype>

DECLARE Age : INTEGER

DECLARE Price : REAL

DECLARE GameOver : BOOLEAN

Python

score = int() # whole number

cost = float() # decimal number

light = bool() # data can only have one or two values

What is a constant?

  • A constant is an identifier set once in the lifetime of a program

  • Constants are named in all uppercase characters

  • Constants aid the readability and maintainability

  • If a constant needs to be changed, it should only need to be altered in one place in the whole program

Pseudocode

CONSTANT <identifier> ← <value>

CONSTANT PI ← 3.142

CONSTANT PASSWORD ← "letmein"

CONSTANT HIGHSCORE ← 9999

Python

PI = 3.142

VAT = 0.20

PASSWORD = "letmein"

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    Robert Hampton

    Author: Robert Hampton

    Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.