Key Terms
- Scope: The region of code where a variable can be seen and used
- Local variable: Declared inside a subprogram; accessible only within that subprogram
- Global variable: Declared outside all subprograms; accessible anywhere in the program
- Lifetime: How long a variable exists — local variables are created when the function runs and destroyed when it ends
Must-Know Facts
- Local variables cannot be accessed outside the subprogram they are declared in
- Global variables exist for the entire runtime of the program
- Local variables are more memory-efficient — they are freed when the function ends
- Parameters are local to the function they belong to
- Best practice: use local variables wherever possible — safer and tidier
- Accessing a local variable outside its function causes a runtime error
Key Concepts
- Declare global:
global score = 0 - Declare local:
local bonus = 10inside a function - Global can be read and modified from any subprogram
- Local is created on function call, destroyed on function return
Common Mistakes
- Trying to use a local variable outside its function: Local variables only exist inside the subprogram where they are declared — accessing them elsewhere causes a runtime error
- Assuming global variables are always better: Global variables can be accidentally modified by any part of the program — local variables are safer and preferred where possible
- Forgetting local variables are destroyed after function ends: Local variables do not retain their value between function calls — a new copy is created each time the function runs
- Confusing scope with data type: Scope (local/global) describes WHERE a variable is accessible; data type (integer/string) describes WHAT it stores — these are separate concepts
Unit 2.3: Robust Programs
This topic summary covers Knowledge Organiser: Variable Scope within Variable Scope for GCSE Computer Science. Revise Variable Scope in 3.2 Programming for GCSE Computer Science with 18 exam-style questions and 10 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 7 of 7 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Variable Scope
Where can a local variable be accessed?
Identify and explain the scope error in this pseudocode: function calculateTotal(price, quantity) local total = price * quantity endfunction calculateTotal(10, 5) output total
Quick recall flashcards
What is variable scope?
Where a variable can be accessed in the code
What is a global variable?
A variable declared outside all subprograms, accessible anywhere in the program