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Edexcel GCSE Computer Science

Programming fundamentals — Edexcel GCSE Computer Science revision

Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 7 minutes to read.

Variables, data types and operators

  • A variable is a named piece of memory whose value can change while a program runs; a constant is set once and never changes, e.g. PI = 3.14.
  • Common data types: integer (whole numbers), real/float (decimals), string (text), Boolean (True/False), character (single letter/symbol).
  • Arithmetic operators: + - * / (division), // or DIV (integer division), MOD or % (remainder), ^ or ** (power).
  • Comparison operators (== != > < >= <=) return a Boolean and are used in selection and iteration conditions.
  • Logical operators AND, OR, NOT combine Boolean conditions, e.g. IF age >= 12 AND hasTicket THEN allowEntry().

Sequence, selection and iteration

  • Sequence means instructions run one after another in order, exactly as written.
  • Selection uses IF/ELSE IF/ELSE (or CASE/SWITCH) to choose which instructions run based on a condition.
  • Count-controlled iteration (FOR loop) repeats a fixed number of times, e.g. FOR i = 1 TO 10.
  • Condition-controlled iteration (WHILE loop) repeats while a condition is true, checked before each pass; REPEAT...UNTIL checks after each pass so it always runs at least once.
  • Nested selection/iteration (loops or IFs inside other loops/IFs) let programs solve more complex problems, e.g. checking every item in every row of a grid.

Key terms

Variable
A named storage location whose value can change while a program runs.
Constant
A named value that is fixed and does not change during execution.
Iteration
Repeating a set of instructions, using FOR, WHILE or REPEAT...UNTIL loops.
Selection
Choosing which code runs using IF, ELSE or CASE statements.
Array
A data structure storing multiple values of the same type under one name, accessed by index.
Parameter
A value passed into a subprogram when it is called.

Common exam traps

  • Confusing = (assignment) with == (comparison) — assignment stores a value, comparison checks equality.
  • Forgetting arrays are usually zero-indexed, so the first element is index 0, not 1.
  • Mixing up WHILE (checks before, may run 0 times) with REPEAT...UNTIL (checks after, runs at least once).

Practice questions with answers

  1. 1. What is a variable?

    • • A named storage location that can change value
    • • A fixed value that never changes
    • • A type of loop
    • • An error message

    Answer: A named storage location that can change value

    Variables store data that can be updated while the program runs.

  2. 2. Which loop always executes its body at least once?

    • • FOR loop
    • • WHILE loop
    • • REPEAT...UNTIL loop
    • • IF statement

    Answer: REPEAT...UNTIL loop

    REPEAT...UNTIL checks its condition after running the body, so it always runs once.

  3. 3. What is the index of the first element in an array?

    Answer: 0

    Most programming languages, including Python, index arrays starting from 0.

  4. 4. Which data type stores True or False?

    • • Integer
    • • Boolean
    • • String
    • • Real

    Answer: Boolean

    Boolean data type has exactly two values: True and False.

  5. 5. What does MOD (or %) return?

    Answer: The remainder after division

    MOD gives the remainder, e.g. 10 MOD 3 = 1.

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